diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -70,8 +70,10 @@
     libc.src.stdlib.strtof
     libc.src.stdlib.strtol
     libc.src.stdlib.strtoll
+    libc.src.stdlib.strtoq
     libc.src.stdlib.strtoul
     libc.src.stdlib.strtoull
+    libc.src.stdlib.strtouq
 )
 
 set(TARGET_LIBM_ENTRYPOINTS
diff --git a/libc/spec/stdc.td b/libc/spec/stdc.td
--- a/libc/spec/stdc.td
+++ b/libc/spec/stdc.td
@@ -510,8 +510,10 @@
           FunctionSpec<"strtof", RetValSpec<FloatType>, [ArgSpec<ConstCharRestrictedPtr>, ArgSpec<CharRestrictedPtrPtr>]>,
           FunctionSpec<"strtol", RetValSpec<LongType>, [ArgSpec<ConstCharRestrictedPtr>, ArgSpec<CharRestrictedPtrPtr>, ArgSpec<IntType>]>,
           FunctionSpec<"strtoll", RetValSpec<LongLongType>, [ArgSpec<ConstCharRestrictedPtr>, ArgSpec<CharRestrictedPtrPtr>, ArgSpec<IntType>]>,
+          FunctionSpec<"strtoq", RetValSpec<LongLongType>, [ArgSpec<ConstCharRestrictedPtr>, ArgSpec<CharRestrictedPtrPtr>, ArgSpec<IntType>]>,
           FunctionSpec<"strtoul", RetValSpec<UnsignedLongType>, [ArgSpec<ConstCharRestrictedPtr>, ArgSpec<CharRestrictedPtrPtr>, ArgSpec<IntType>]>,
           FunctionSpec<"strtoull", RetValSpec<UnsignedLongLongType>, [ArgSpec<ConstCharRestrictedPtr>, ArgSpec<CharRestrictedPtrPtr>, ArgSpec<IntType>]>,
+          FunctionSpec<"strtouq", RetValSpec<UnsignedLongLongType>, [ArgSpec<ConstCharRestrictedPtr>, ArgSpec<CharRestrictedPtrPtr>, ArgSpec<IntType>]>,
 
           FunctionSpec<"_Exit", RetValSpec<NoReturn>, [ArgSpec<IntType>]>,
       ]
diff --git a/libc/src/stdlib/CMakeLists.txt b/libc/src/stdlib/CMakeLists.txt
--- a/libc/src/stdlib/CMakeLists.txt
+++ b/libc/src/stdlib/CMakeLists.txt
@@ -78,6 +78,16 @@
     libc.src.__support.str_conv_utils
 )
 
+add_entrypoint_object(
+  strtoq
+  SRCS
+    strtoq.cpp
+  HDRS
+    strtoq.h
+  DEPENDS
+    libc.src.__support.str_conv_utils
+)
+
 add_entrypoint_object(
   strtoul
   SRCS
@@ -98,6 +108,16 @@
     libc.src.__support.str_conv_utils
 )
 
+add_entrypoint_object(
+  strtouq
+  SRCS
+    strtouq.cpp
+  HDRS
+    strtouq.h
+  DEPENDS
+    libc.src.__support.str_conv_utils
+)
+
 add_entrypoint_object(
   abs
   SRCS
diff --git a/libc/src/stdlib/strtoq.h b/libc/src/stdlib/strtoq.h
new file mode 100644
--- /dev/null
+++ b/libc/src/stdlib/strtoq.h
@@ -0,0 +1,19 @@
+//===-- Implementation header for strtoq ------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDLIB_STRTOQ_H
+#define LLVM_LIBC_SRC_STDLIB_STRTOQ_H
+
+namespace __llvm_libc {
+
+long long strtoq(const char *__restrict str, char **__restrict str_end,
+                 int base);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_STDLIB_STRTOQ_H
diff --git a/libc/src/stdlib/strtoq.cpp b/libc/src/stdlib/strtoq.cpp
new file mode 100644
--- /dev/null
+++ b/libc/src/stdlib/strtoq.cpp
@@ -0,0 +1,21 @@
+//===-- Implementation of strtoq -----------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdlib/strtoq.h"
+#include "src/__support/common.h"
+#include "src/__support/str_conv_utils.h"
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(long long, strtoq,
+                   (const char *__restrict str, char **__restrict str_end,
+                    int base)) {
+  return internal::strtointeger<long long>(str, str_end, base);
+}
+
+} // namespace __llvm_libc
diff --git a/libc/src/stdlib/strtouq.h b/libc/src/stdlib/strtouq.h
new file mode 100644
--- /dev/null
+++ b/libc/src/stdlib/strtouq.h
@@ -0,0 +1,19 @@
+//===-- Implementation header for strtouq -----------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDLIB_STRTOUQ_H
+#define LLVM_LIBC_SRC_STDLIB_STRTOUQ_H
+
+namespace __llvm_libc {
+
+unsigned long long strtouq(const char *__restrict str,
+                           char **__restrict str_end, int base);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_STDLIB_STRTOUQ_H
diff --git a/libc/src/stdlib/strtouq.cpp b/libc/src/stdlib/strtouq.cpp
new file mode 100644
--- /dev/null
+++ b/libc/src/stdlib/strtouq.cpp
@@ -0,0 +1,21 @@
+//===-- Implementation of strtouq -----------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdlib/strtouq.h"
+#include "src/__support/common.h"
+#include "src/__support/str_conv_utils.h"
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(unsigned long long, strtouq,
+                   (const char *__restrict str, char **__restrict str_end,
+                    int base)) {
+  return internal::strtointeger<unsigned long long>(str, str_end, base);
+}
+
+} // namespace __llvm_libc
diff --git a/libc/test/src/stdlib/CMakeLists.txt b/libc/test/src/stdlib/CMakeLists.txt
--- a/libc/test/src/stdlib/CMakeLists.txt
+++ b/libc/test/src/stdlib/CMakeLists.txt
@@ -80,6 +80,16 @@
     libc.src.stdlib.strtoll
 )
 
+add_libc_unittest(
+  strtoq_test
+  SUITE
+    libc_stdlib_unittests
+  SRCS
+    strtoq_test.cpp
+  DEPENDS
+    libc.src.stdlib.strtoq
+)
+
 add_libc_unittest(
   strtoul_test
   SUITE
@@ -100,6 +110,16 @@
     libc.src.stdlib.strtoull
 )
 
+add_libc_unittest(
+  strtouq_test
+  SUITE
+    libc_stdlib_unittests
+  SRCS
+    strtouq_test.cpp
+  DEPENDS
+    libc.src.stdlib.strtouq
+)
+
 if(NOT LLVM_LIBC_FULL_BUILD)
   return()
 endif()
diff --git a/libc/test/src/stdlib/strtoq_test.cpp b/libc/test/src/stdlib/strtoq_test.cpp
new file mode 100644
--- /dev/null
+++ b/libc/test/src/stdlib/strtoq_test.cpp
@@ -0,0 +1,26 @@
+//===-- Unittests for strtoq ----------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdlib/strtoq.h"
+
+#include "utils/UnitTest/Test.h"
+
+#include <errno.h>
+#include <limits.h>
+#include <stddef.h>
+
+// strtoq is equivalent to strtoll on all currently supported configurations.
+// Thus to avoid duplicating code there is just one test to make sure that
+// strtoq works at all. For real tests see stdlib/strtoll_test.cpp.
+
+TEST(LlvmLibcStrToQTest, SimpleCheck) {
+  const char *ten = "10";
+  errno = 0;
+  ASSERT_EQ(__llvm_libc::strtoq(ten, nullptr, 10), 10ll);
+  ASSERT_EQ(errno, 0);
+}
diff --git a/libc/test/src/stdlib/strtouq_test.cpp b/libc/test/src/stdlib/strtouq_test.cpp
new file mode 100644
--- /dev/null
+++ b/libc/test/src/stdlib/strtouq_test.cpp
@@ -0,0 +1,26 @@
+//===-- Unittests for strtouq -------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdlib/strtouq.h"
+
+#include "utils/UnitTest/Test.h"
+
+#include <errno.h>
+#include <limits.h>
+#include <stddef.h>
+
+// strtouq is equivalent to strtoull on all currently supported configurations.
+// Thus to avoid duplicating code there is just one test to make sure that
+// strtouq works at all. For real tests see stdlib/strtoull_test.cpp.
+
+TEST(LlvmLibcStrToUQTest, SimpleCheck) {
+  const char *ten = "10";
+  errno = 0;
+  ASSERT_EQ(__llvm_libc::strtouq(ten, nullptr, 10), 10ull);
+  ASSERT_EQ(errno, 0);
+}