diff --git a/libc/src/signal/linux/CMakeLists.txt b/libc/src/signal/linux/CMakeLists.txt
--- a/libc/src/signal/linux/CMakeLists.txt
+++ b/libc/src/signal/linux/CMakeLists.txt
@@ -15,7 +15,6 @@
     ../kill.h
   DEPENDS
     libc.include.signal
-    libc.include.errno
     libc.src.errno.errno
     libc.include.sys_syscall
     libc.src.__support.OSUtil.osutil
@@ -100,7 +99,6 @@
     ../sigemptyset.h
   DEPENDS
     .signal_utils
-    libc.include.errno
     libc.include.signal
     libc.src.errno.errno
 )
@@ -113,7 +111,6 @@
     ../sigaddset.h
   DEPENDS
     .signal_utils
-    libc.include.errno
     libc.include.signal
     libc.src.errno.errno
 )
@@ -137,7 +134,6 @@
     ../sigfillset.h
   DEPENDS
     .signal_utils
-    libc.include.errno
     libc.include.signal
     libc.src.errno.errno
 )
@@ -150,7 +146,6 @@
     ../sigdelset.h
   DEPENDS
     .signal_utils
-    libc.include.errno
     libc.include.signal
     libc.src.errno.errno
 )
diff --git a/libc/src/signal/linux/kill.cpp b/libc/src/signal/linux/kill.cpp
--- a/libc/src/signal/linux/kill.cpp
+++ b/libc/src/signal/linux/kill.cpp
@@ -9,11 +9,10 @@
 #include "src/signal/kill.h"
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
-#include "src/signal/linux/signal_utils.h"
-
 #include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
+#include "src/signal/linux/signal_utils.h"
 
-#include <errno.h>
 #include <signal.h>
 #include <sys/syscall.h> // For syscall numbers.
 
@@ -25,7 +24,7 @@
   // A negative return value indicates an error with the magnitude of the
   // value being the error code.
   if (ret != 0) {
-    errno = (ret > 0 ? ret : -ret);
+    libc_errno = (ret > 0 ? ret : -ret);
     return -1;
   }
 
diff --git a/libc/src/signal/linux/sigaction.cpp b/libc/src/signal/linux/sigaction.cpp
--- a/libc/src/signal/linux/sigaction.cpp
+++ b/libc/src/signal/linux/sigaction.cpp
@@ -7,11 +7,11 @@
 //===----------------------------------------------------------------------===//
 
 #include "src/signal/sigaction.h"
+#include "src/errno/libc_errno.h"
 #include "src/signal/linux/signal_utils.h"
 
 #include "src/__support/common.h"
 
-#include <errno.h>
 #include <signal.h>
 
 namespace __llvm_libc {
@@ -38,7 +38,7 @@
       SYS_rt_sigaction, signal, libc_new ? &kernel_new : nullptr,
       libc_old ? &kernel_old : nullptr, sizeof(sigset_t));
   if (ret) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
 
diff --git a/libc/src/signal/linux/sigaddset.cpp b/libc/src/signal/linux/sigaddset.cpp
--- a/libc/src/signal/linux/sigaddset.cpp
+++ b/libc/src/signal/linux/sigaddset.cpp
@@ -8,9 +8,9 @@
 
 #include "src/signal/sigaddset.h"
 #include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
 #include "src/signal/linux/signal_utils.h"
 
-#include <errno.h>
 #include <signal.h>
 
 namespace __llvm_libc {
@@ -18,7 +18,7 @@
 LLVM_LIBC_FUNCTION(int, sigaddset, (sigset_t * set, int signum)) {
   if (set != nullptr && add_signal(*set, signum))
     return 0;
-  errno = EINVAL;
+  libc_errno = EINVAL;
   return -1;
 }
 
diff --git a/libc/src/signal/linux/sigaltstack.cpp b/libc/src/signal/linux/sigaltstack.cpp
--- a/libc/src/signal/linux/sigaltstack.cpp
+++ b/libc/src/signal/linux/sigaltstack.cpp
@@ -7,11 +7,11 @@
 //===----------------------------------------------------------------------===//
 
 #include "src/signal/sigaltstack.h"
+#include "src/errno/libc_errno.h"
 #include "src/signal/linux/signal_utils.h"
 
 #include "src/__support/common.h"
 
-#include <errno.h>
 #include <signal.h>
 #include <sys/syscall.h>
 
@@ -25,18 +25,18 @@
       // Flags cannot have anything other than SS_DISABLE set.
       // We do the type-casting to unsigned because the |ss_flags|
       // field of stack_t is of type "int".
-      errno = EINVAL;
+      libc_errno = EINVAL;
       return -1;
     }
     if (ss->ss_size < MINSIGSTKSZ) {
-      errno = ENOMEM;
+      libc_errno = ENOMEM;
       return -1;
     }
   }
 
   int ret = __llvm_libc::syscall_impl(SYS_sigaltstack, ss, oss);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return 0;
diff --git a/libc/src/signal/linux/sigdelset.cpp b/libc/src/signal/linux/sigdelset.cpp
--- a/libc/src/signal/linux/sigdelset.cpp
+++ b/libc/src/signal/linux/sigdelset.cpp
@@ -8,9 +8,9 @@
 
 #include "src/signal/sigdelset.h"
 #include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
 #include "src/signal/linux/signal_utils.h"
 
-#include <errno.h>
 #include <signal.h>
 
 namespace __llvm_libc {
@@ -18,7 +18,7 @@
 LLVM_LIBC_FUNCTION(int, sigdelset, (sigset_t * set, int signum)) {
   if (set != nullptr && delete_signal(*set, signum))
     return 0;
-  errno = EINVAL;
+  libc_errno = EINVAL;
   return -1;
 }
 
diff --git a/libc/src/signal/linux/sigemptyset.cpp b/libc/src/signal/linux/sigemptyset.cpp
--- a/libc/src/signal/linux/sigemptyset.cpp
+++ b/libc/src/signal/linux/sigemptyset.cpp
@@ -7,18 +7,18 @@
 //===----------------------------------------------------------------------===//
 
 #include "src/signal/sigemptyset.h"
+#include "src/errno/libc_errno.h"
 #include "src/signal/linux/signal_utils.h"
 
 #include "src/__support/common.h"
 
-#include <errno.h>
 #include <signal.h>
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, sigemptyset, (sigset_t * set)) {
   if (!set) {
-    errno = EINVAL;
+    libc_errno = EINVAL;
     return -1;
   }
   *set = empty_set();
diff --git a/libc/src/signal/linux/sigfillset.cpp b/libc/src/signal/linux/sigfillset.cpp
--- a/libc/src/signal/linux/sigfillset.cpp
+++ b/libc/src/signal/linux/sigfillset.cpp
@@ -8,16 +8,16 @@
 
 #include "src/signal/sigfillset.h"
 #include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
 #include "src/signal/linux/signal_utils.h"
 
-#include <errno.h>
 #include <signal.h>
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, sigfillset, (sigset_t * set)) {
   if (!set) {
-    errno = EINVAL;
+    libc_errno = EINVAL;
     return -1;
   }
   *set = full_set();
diff --git a/libc/src/signal/linux/sigprocmask.cpp b/libc/src/signal/linux/sigprocmask.cpp
--- a/libc/src/signal/linux/sigprocmask.cpp
+++ b/libc/src/signal/linux/sigprocmask.cpp
@@ -9,11 +9,11 @@
 #include "src/signal/sigprocmask.h"
 #include "include/sys/syscall.h"          // For syscall numbers.
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/errno/libc_errno.h"
 #include "src/signal/linux/signal_utils.h"
 
 #include "src/__support/common.h"
 
-#include <errno.h>
 #include <signal.h>
 
 namespace __llvm_libc {
@@ -26,7 +26,7 @@
   if (!ret)
     return 0;
 
-  errno = -ret;
+  libc_errno = -ret;
   return -1;
 }
 
diff --git a/libc/src/termios/linux/cfsetispeed.cpp b/libc/src/termios/linux/cfsetispeed.cpp
--- a/libc/src/termios/linux/cfsetispeed.cpp
+++ b/libc/src/termios/linux/cfsetispeed.cpp
@@ -9,8 +9,8 @@
 #include "src/termios/cfsetispeed.h"
 
 #include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
 
-#include <errno.h>
 #include <termios.h>
 
 namespace __llvm_libc {
@@ -19,7 +19,7 @@
   constexpr speed_t NOT_SPEED_MASK = ~speed_t(CBAUD);
   // A speed value is valid only if it is equal to one of the B<NN+> values.
   if (t == nullptr || ((speed & NOT_SPEED_MASK) != 0)) {
-    errno = EINVAL;
+    libc_errno = EINVAL;
     return -1;
   }
 
diff --git a/libc/src/termios/linux/cfsetospeed.cpp b/libc/src/termios/linux/cfsetospeed.cpp
--- a/libc/src/termios/linux/cfsetospeed.cpp
+++ b/libc/src/termios/linux/cfsetospeed.cpp
@@ -7,10 +7,10 @@
 //===----------------------------------------------------------------------===//
 
 #include "src/termios/cfsetospeed.h"
+#include "src/errno/libc_errno.h"
 
 #include "src/__support/common.h"
 
-#include <errno.h>
 #include <termios.h>
 
 namespace __llvm_libc {
@@ -19,7 +19,7 @@
   constexpr speed_t NOT_SPEED_MASK = ~speed_t(CBAUD);
   // A speed value is valid only if it is equal to one of the B<NN+> values.
   if (t == nullptr || ((speed & NOT_SPEED_MASK) != 0)) {
-    errno = EINVAL;
+    libc_errno = EINVAL;
     return -1;
   }
 
diff --git a/libc/src/termios/linux/tcdrain.cpp b/libc/src/termios/linux/tcdrain.cpp
--- a/libc/src/termios/linux/tcdrain.cpp
+++ b/libc/src/termios/linux/tcdrain.cpp
@@ -10,9 +10,9 @@
 
 #include "src/__support/OSUtil/syscall.h"
 #include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
 
 #include <asm/ioctls.h> // Safe to include without the risk of name pollution.
-#include <errno.h>
 #include <sys/syscall.h> // For syscall numbers
 #include <termios.h>
 
diff --git a/libc/src/termios/linux/tcflow.cpp b/libc/src/termios/linux/tcflow.cpp
--- a/libc/src/termios/linux/tcflow.cpp
+++ b/libc/src/termios/linux/tcflow.cpp
@@ -10,9 +10,9 @@
 
 #include "src/__support/OSUtil/syscall.h"
 #include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
 
 #include <asm/ioctls.h> // Safe to include without the risk of name pollution.
-#include <errno.h>
 #include <sys/syscall.h> // For syscall numbers
 #include <termios.h>
 
@@ -21,7 +21,7 @@
 LLVM_LIBC_FUNCTION(int, tcflow, (int fd, int action)) {
   long ret = __llvm_libc::syscall_impl(SYS_ioctl, fd, TCXONC, action);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return 0;
diff --git a/libc/src/termios/linux/tcflush.cpp b/libc/src/termios/linux/tcflush.cpp
--- a/libc/src/termios/linux/tcflush.cpp
+++ b/libc/src/termios/linux/tcflush.cpp
@@ -10,9 +10,9 @@
 
 #include "src/__support/OSUtil/syscall.h"
 #include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
 
 #include <asm/ioctls.h> // Safe to include without the risk of name pollution.
-#include <errno.h>
 #include <sys/syscall.h> // For syscall numbers
 #include <termios.h>
 
diff --git a/libc/src/termios/linux/tcgetattr.cpp b/libc/src/termios/linux/tcgetattr.cpp
--- a/libc/src/termios/linux/tcgetattr.cpp
+++ b/libc/src/termios/linux/tcgetattr.cpp
@@ -11,9 +11,9 @@
 
 #include "src/__support/OSUtil/syscall.h"
 #include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
 
 #include <asm/ioctls.h> // Safe to include without the risk of name pollution.
-#include <errno.h>
 #include <sys/syscall.h> // For syscall numbers
 #include <termios.h>
 
@@ -23,7 +23,7 @@
   __llvm_libc::kernel_termios kt;
   long ret = __llvm_libc::syscall_impl(SYS_ioctl, fd, TCGETS, &kt);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   t->c_iflag = kt.c_iflag;
diff --git a/libc/src/termios/linux/tcgetsid.cpp b/libc/src/termios/linux/tcgetsid.cpp
--- a/libc/src/termios/linux/tcgetsid.cpp
+++ b/libc/src/termios/linux/tcgetsid.cpp
@@ -10,9 +10,9 @@
 
 #include "src/__support/OSUtil/syscall.h"
 #include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
 
 #include <asm/ioctls.h> // Safe to include without the risk of name pollution.
-#include <errno.h>
 #include <sys/syscall.h> // For syscall numbers
 #include <termios.h>
 
diff --git a/libc/src/termios/linux/tcsendbreak.cpp b/libc/src/termios/linux/tcsendbreak.cpp
--- a/libc/src/termios/linux/tcsendbreak.cpp
+++ b/libc/src/termios/linux/tcsendbreak.cpp
@@ -10,9 +10,9 @@
 
 #include "src/__support/OSUtil/syscall.h"
 #include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
 
 #include <asm/ioctls.h> // Safe to include without the risk of name pollution.
-#include <errno.h>
 #include <sys/syscall.h> // For syscall numbers
 #include <termios.h>
 
@@ -24,7 +24,7 @@
   // zero. So, we just pass zero to the syscall.
   long ret = __llvm_libc::syscall_impl(SYS_ioctl, fd, TCSBRK, 0);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return 0;
diff --git a/libc/src/termios/linux/tcsetattr.cpp b/libc/src/termios/linux/tcsetattr.cpp
--- a/libc/src/termios/linux/tcsetattr.cpp
+++ b/libc/src/termios/linux/tcsetattr.cpp
@@ -11,9 +11,9 @@
 
 #include "src/__support/OSUtil/syscall.h"
 #include "src/__support/common.h"
+#include "src/errno/libc_errno.h"
 
 #include <asm/ioctls.h> // Safe to include without the risk of name pollution.
-#include <errno.h>
 #include <sys/syscall.h> // For syscall numbers
 #include <termios.h>
 
@@ -35,7 +35,7 @@
     cmd = TCSETSF;
     break;
   default:
-    errno = EINVAL;
+    libc_errno = EINVAL;
     return -1;
   }
 
@@ -53,7 +53,7 @@
 
   long ret = __llvm_libc::syscall_impl(SYS_ioctl, fd, cmd, &kt);
   if (ret < 0) {
-    errno = -ret;
+    libc_errno = -ret;
     return -1;
   }
   return 0;
diff --git a/libc/test/src/signal/CMakeLists.txt b/libc/test/src/signal/CMakeLists.txt
--- a/libc/test/src/signal/CMakeLists.txt
+++ b/libc/test/src/signal/CMakeLists.txt
@@ -19,8 +19,6 @@
     kill_test.cpp
   DEPENDS
     libc.include.signal
-    libc.include.errno
-    libc.src.errno.errno
     libc.src.signal.kill
     libc.include.sys_syscall
     libc.src.__support.OSUtil.osutil
@@ -48,7 +46,6 @@
   SRCS
     sigprocmask_test.cpp
   DEPENDS
-    libc.include.errno
     libc.src.errno.errno
     libc.src.signal.raise
     libc.src.signal.sigaddset
@@ -77,7 +74,6 @@
   SRCS
     signal_test.cpp
   DEPENDS
-    libc.include.errno
     libc.include.signal
     libc.src.errno.errno
     libc.src.signal.raise
@@ -123,9 +119,10 @@
   SRCS
     sigaltstack_test.cpp
   DEPENDS
-    libc.include.errno
     libc.include.signal
+    libc.src.errno.errno
     libc.src.signal.raise
     libc.src.signal.sigaltstack
     libc.src.signal.sigaction
+    libc.test.errno_setter_matcher
 )
diff --git a/libc/test/src/signal/kill_test.cpp b/libc/test/src/signal/kill_test.cpp
--- a/libc/test/src/signal/kill_test.cpp
+++ b/libc/test/src/signal/kill_test.cpp
@@ -13,7 +13,6 @@
 #include "test/ErrnoSetterMatcher.h"
 #include "test/UnitTest/Test.h"
 
-#include <errno.h>
 #include <signal.h>
 
 using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
diff --git a/libc/test/src/signal/sigaddset_test.cpp b/libc/test/src/signal/sigaddset_test.cpp
--- a/libc/test/src/signal/sigaddset_test.cpp
+++ b/libc/test/src/signal/sigaddset_test.cpp
@@ -6,13 +6,14 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "include/errno.h"
 #include "include/signal.h"
 #include "src/signal/sigaddset.h"
 
 #include "test/ErrnoSetterMatcher.h"
 #include "test/UnitTest/Test.h"
 
+#include <errno.h>
+
 // This tests invalid inputs and ensures errno is properly set.
 TEST(LlvmLibcSignalTest, SigaddsetInvalid) {
   using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
diff --git a/libc/test/src/signal/sigaltstack_test.cpp b/libc/test/src/signal/sigaltstack_test.cpp
--- a/libc/test/src/signal/sigaltstack_test.cpp
+++ b/libc/test/src/signal/sigaltstack_test.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "src/__support/OSUtil/syscall.h" // For internal syscall function.
+#include "src/errno/libc_errno.h"
 #include "src/signal/linux/signal_utils.h"
 #include "src/signal/raise.h"
 #include "src/signal/sigaction.h"
@@ -15,7 +16,6 @@
 #include "test/ErrnoSetterMatcher.h"
 #include "test/UnitTest/Test.h"
 
-#include <errno.h>
 #include <signal.h>
 #include <stdint.h>
 #include <sys/syscall.h>
@@ -47,7 +47,7 @@
 
 TEST(LlvmLibcSignalTest, SigaltstackRunOnAltStack) {
   struct sigaction action;
-  errno = 0;
+  libc_errno = 0;
   ASSERT_THAT(__llvm_libc::sigaction(SIGUSR1, nullptr, &action), Succeeds(0));
   action.sa_handler = handler;
   // Indicate that the signal should be delivered on an alternate stack.
diff --git a/libc/test/src/signal/sigdelset_test.cpp b/libc/test/src/signal/sigdelset_test.cpp
--- a/libc/test/src/signal/sigdelset_test.cpp
+++ b/libc/test/src/signal/sigdelset_test.cpp
@@ -6,7 +6,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "include/errno.h"
 #include "include/signal.h"
 #include "src/signal/raise.h"
 #include "src/signal/sigdelset.h"
@@ -16,6 +15,8 @@
 #include "test/ErrnoSetterMatcher.h"
 #include "test/UnitTest/Test.h"
 
+#include <errno.h>
+
 TEST(LlvmLibcSigdelset, Invalid) {
   using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
   // Invalid set.
diff --git a/libc/test/src/signal/sigfillset_test.cpp b/libc/test/src/signal/sigfillset_test.cpp
--- a/libc/test/src/signal/sigfillset_test.cpp
+++ b/libc/test/src/signal/sigfillset_test.cpp
@@ -6,7 +6,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "include/errno.h"
 #include "include/signal.h"
 #include "src/signal/raise.h"
 #include "src/signal/sigfillset.h"
@@ -15,6 +14,8 @@
 #include "test/ErrnoSetterMatcher.h"
 #include "test/UnitTest/Test.h"
 
+#include <errno.h>
+
 TEST(LlvmLibcSigfillset, Invalid) {
   using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
   EXPECT_THAT(__llvm_libc::sigfillset(nullptr), Fails(EINVAL));
diff --git a/libc/test/src/signal/signal_test.cpp b/libc/test/src/signal/signal_test.cpp
--- a/libc/test/src/signal/signal_test.cpp
+++ b/libc/test/src/signal/signal_test.cpp
@@ -6,9 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "include/errno.h"
 #include "include/signal.h"
-#include "src/errno/llvmlibc_errno.h"
+#include "src/errno/libc_errno.h"
 #include "src/signal/raise.h"
 #include "src/signal/signal.h"
 
@@ -19,7 +18,7 @@
 using __llvm_libc::testing::ErrnoSetterMatcher::Succeeds;
 
 TEST(LlvmLibcSignal, Invalid) {
-  llvmlibc_errno = 0;
+  libc_errno = 0;
   __llvm_libc::sighandler_t valid = +[](int) {};
   EXPECT_THAT((void *)__llvm_libc::signal(0, valid),
               Fails(EINVAL, (void *)SIG_ERR));
diff --git a/libc/test/src/signal/sigprocmask_test.cpp b/libc/test/src/signal/sigprocmask_test.cpp
--- a/libc/test/src/signal/sigprocmask_test.cpp
+++ b/libc/test/src/signal/sigprocmask_test.cpp
@@ -6,9 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "include/errno.h"
 #include "include/signal.h"
-#include "src/errno/llvmlibc_errno.h"
+#include "src/errno/libc_errno.h"
 #include "src/signal/raise.h"
 #include "src/signal/sigaddset.h"
 #include "src/signal/sigemptyset.h"
@@ -33,7 +32,7 @@
 
 // This tests for invalid input.
 TEST_F(LlvmLibcSignalTest, SigprocmaskInvalid) {
-  llvmlibc_errno = 0;
+  libc_errno = 0;
 
   sigset_t valid;
   // 17 and -4 are out of the range for sigprocmask's how paramater.
diff --git a/libc/test/src/termios/CMakeLists.txt b/libc/test/src/termios/CMakeLists.txt
--- a/libc/test/src/termios/CMakeLists.txt
+++ b/libc/test/src/termios/CMakeLists.txt
@@ -7,8 +7,8 @@
   SRCS
     termios_test.cpp
   DEPENDS
-    libc.include.errno
     libc.include.termios
+    libc.src.errno.errno
     libc.src.fcntl.open
     libc.src.termios.cfgetispeed
     libc.src.termios.cfgetospeed
diff --git a/libc/test/src/termios/termios_test.cpp b/libc/test/src/termios/termios_test.cpp
--- a/libc/test/src/termios/termios_test.cpp
+++ b/libc/test/src/termios/termios_test.cpp
@@ -6,6 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "src/errno/libc_errno.h"
 #include "src/fcntl/open.h"
 #include "src/termios/cfgetispeed.h"
 #include "src/termios/cfgetospeed.h"
@@ -18,7 +19,6 @@
 #include "test/ErrnoSetterMatcher.h"
 #include "test/UnitTest/Test.h"
 
-#include <errno.h>
 #include <termios.h>
 
 using __llvm_libc::testing::ErrnoSetterMatcher::Fails;
@@ -30,35 +30,35 @@
 
 TEST(LlvmLibcTermiosTest, SpeedSmokeTest) {
   struct termios t;
-  errno = 0;
+  libc_errno = 0;
   ASSERT_THAT(__llvm_libc::cfsetispeed(&t, B50), Succeeds(0));
   ASSERT_EQ(__llvm_libc::cfgetispeed(&t), speed_t(B50));
   ASSERT_THAT(__llvm_libc::cfsetospeed(&t, B75), Succeeds(0));
   ASSERT_EQ(__llvm_libc::cfgetospeed(&t), speed_t(B75));
 
-  errno = 0;
+  libc_errno = 0;
   ASSERT_THAT(__llvm_libc::cfsetispeed(&t, ~CBAUD), Fails(EINVAL));
-  errno = 0;
+  libc_errno = 0;
   ASSERT_THAT(__llvm_libc::cfsetospeed(&t, ~CBAUD), Fails(EINVAL));
 }
 
 TEST(LlvmLibcTermiosTest, GetAttrSmokeTest) {
   struct termios t;
-  errno = 0;
+  libc_errno = 0;
   int fd = __llvm_libc::open("/dev/tty", O_RDONLY);
   if (fd < 0)
     return; // When /dev/tty is not available, no point continuing.
-  ASSERT_EQ(errno, 0);
+  ASSERT_EQ(libc_errno, 0);
   ASSERT_THAT(__llvm_libc::tcgetattr(fd, &t), Succeeds(0));
   ASSERT_EQ(__llvm_libc::close(fd), 0);
 }
 
 TEST(LlvmLibcTermiosTest, TcGetSidSmokeTest) {
-  errno = 0;
+  libc_errno = 0;
   int fd = __llvm_libc::open("/dev/tty", O_RDONLY);
   if (fd < 0)
     return; // When /dev/tty is not available, no point continuing.
-  ASSERT_EQ(errno, 0);
+  ASSERT_EQ(libc_errno, 0);
   ASSERT_GT(__llvm_libc::tcgetsid(fd), pid_t(0));
   ASSERT_EQ(__llvm_libc::close(fd), 0);
 }