diff --git a/libc/src/ctype/isblank.cpp b/libc/src/ctype/isblank.cpp
--- a/libc/src/ctype/isblank.cpp
+++ b/libc/src/ctype/isblank.cpp
@@ -15,8 +15,7 @@
 // TODO: Currently restricted to default locale.
 // These should be extended using locale information.
 LLVM_LIBC_FUNCTION(int, isblank, (int c)) {
-  const unsigned char ch = static_cast<unsigned char>(c);
-  return static_cast<int>(ch == ' ' || ch == '\t');
+  return static_cast<int>(c == ' ' || c == '\t');
 }
 
 } // namespace __llvm_libc
diff --git a/libc/src/ctype/iscntrl.cpp b/libc/src/ctype/iscntrl.cpp
--- a/libc/src/ctype/iscntrl.cpp
+++ b/libc/src/ctype/iscntrl.cpp
@@ -15,7 +15,7 @@
 // TODO: Currently restricted to default locale.
 // These should be extended using locale information.
 LLVM_LIBC_FUNCTION(int, iscntrl, (int c)) {
-  const unsigned char ch = static_cast<unsigned char>(c);
+  const unsigned ch = static_cast<unsigned>(c);
   return static_cast<int>(ch < 0x20 || ch == 0x7f);
 }
 
diff --git a/libc/test/src/ctype/CMakeLists.txt b/libc/test/src/ctype/CMakeLists.txt
--- a/libc/test/src/ctype/CMakeLists.txt
+++ b/libc/test/src/ctype/CMakeLists.txt
@@ -1,7 +1,7 @@
 add_libc_testsuite(libc_ctype_unittests)
 
 add_libc_unittest(
-  isalnum
+  isalnum_test
   SUITE
     libc_ctype_unittests
   SRCS
@@ -11,7 +11,7 @@
 )
 
 add_libc_unittest(
-  isalpha
+  isalpha_test
   SUITE
     libc_ctype_unittests
   SRCS
@@ -21,7 +21,7 @@
 )
 
 add_libc_unittest(
-  isascii
+  isascii_test
   SUITE
     libc_ctype_unittests
   SRCS
@@ -31,7 +31,7 @@
 )
 
 add_libc_unittest(
-  isblank
+  isblank_test
   SUITE
     libc_ctype_unittests
   SRCS
@@ -41,7 +41,7 @@
 )
 
 add_libc_unittest(
-  iscntrl
+  iscntrl_test
   SUITE
     libc_ctype_unittests
   SRCS
@@ -51,7 +51,7 @@
 )
 
 add_libc_unittest(
-  isdigit
+  isdigit_test
   SUITE
     libc_ctype_unittests
   SRCS
@@ -61,7 +61,7 @@
 )
 
 add_libc_unittest(
-  isgraph
+  isgraph_test
   SUITE
     libc_ctype_unittests
   SRCS
@@ -71,7 +71,7 @@
 )
 
 add_libc_unittest(
-  islower
+  islower_test
   SUITE
     libc_ctype_unittests
   SRCS
@@ -81,7 +81,7 @@
 )
 
 add_libc_unittest(
-  isprint
+  isprint_test
   SUITE
     libc_ctype_unittests
   SRCS
@@ -91,7 +91,7 @@
 )
 
 add_libc_unittest(
-  ispunct
+  ispunct_test
   SUITE
     libc_ctype_unittests
   SRCS
@@ -101,7 +101,7 @@
 )
 
 add_libc_unittest(
-  isspace
+  isspace_test
   SUITE
     libc_ctype_unittests
   SRCS
@@ -111,7 +111,7 @@
 )
 
 add_libc_unittest(
-  isupper
+  isupper_test
   SUITE
     libc_ctype_unittests
   SRCS
@@ -121,7 +121,7 @@
 )
 
 add_libc_unittest(
-  isxdigit
+  isxdigit_test
   SUITE
     libc_ctype_unittests
   SRCS
@@ -131,7 +131,7 @@
 )
 
 add_libc_unittest(
-  toascii
+  toascii_test
   SUITE
     libc_ctype_unittests
   SRCS
@@ -141,7 +141,7 @@
 )
 
 add_libc_unittest(
-  tolower
+  tolower_test
   SUITE
     libc_ctype_unittests
   SRCS
@@ -151,7 +151,7 @@
 )
 
 add_libc_unittest(
-  toupper
+  toupper_test
   SUITE
     libc_ctype_unittests
   SRCS
diff --git a/libc/test/src/ctype/isalnum_test.cpp b/libc/test/src/ctype/isalnum_test.cpp
--- a/libc/test/src/ctype/isalnum_test.cpp
+++ b/libc/test/src/ctype/isalnum_test.cpp
@@ -13,7 +13,7 @@
 TEST(LlvmLibcIsAlNum, DefaultLocale) {
   // Loops through all characters, verifying that numbers and letters
   // return non-zero integer and everything else returns a zero.
-  for (int c = 0; c < 255; ++c) {
+  for (int c = -255; c < 255; ++c) {
     if (('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z') ||
         ('0' <= c && c <= '9'))
       EXPECT_NE(__llvm_libc::isalnum(c), 0);
diff --git a/libc/test/src/ctype/isalpha_test.cpp b/libc/test/src/ctype/isalpha_test.cpp
--- a/libc/test/src/ctype/isalpha_test.cpp
+++ b/libc/test/src/ctype/isalpha_test.cpp
@@ -13,7 +13,7 @@
 TEST(LlvmLibcIsAlpha, DefaultLocale) {
   // Loops through all characters, verifying that letters return a
   // non-zero integer and everything else returns zero.
-  for (int ch = 0; ch < 255; ++ch) {
+  for (int ch = -255; ch < 255; ++ch) {
     if (('a' <= ch && ch <= 'z') || ('A' <= ch && ch <= 'Z'))
       EXPECT_NE(__llvm_libc::isalpha(ch), 0);
     else
diff --git a/libc/test/src/ctype/isascii_test.cpp b/libc/test/src/ctype/isascii_test.cpp
--- a/libc/test/src/ctype/isascii_test.cpp
+++ b/libc/test/src/ctype/isascii_test.cpp
@@ -14,8 +14,8 @@
   // Loops through all characters, verifying that ascii characters
   //    (which are all 7 bit unsigned integers)
   // return a non-zero integer and everything else returns zero.
-  for (int ch = 0; ch < 255; ++ch) {
-    if (ch <= 0x7f)
+  for (int ch = -255; ch < 255; ++ch) {
+    if (0 <= ch && ch <= 0x7f)
       EXPECT_NE(__llvm_libc::isascii(ch), 0);
     else
       EXPECT_EQ(__llvm_libc::isascii(ch), 0);
diff --git a/libc/test/src/ctype/isblank_test.cpp b/libc/test/src/ctype/isblank_test.cpp
--- a/libc/test/src/ctype/isblank_test.cpp
+++ b/libc/test/src/ctype/isblank_test.cpp
@@ -12,7 +12,7 @@
 TEST(LlvmLibcIsBlank, DefaultLocale) {
   // Loops through all characters, verifying that space and horizontal tab
   // return a non-zero integer and everything else returns zero.
-  for (int ch = 0; ch < 255; ++ch) {
+  for (int ch = -255; ch < 255; ++ch) {
     if (ch == ' ' || ch == '\t')
       EXPECT_NE(__llvm_libc::isblank(ch), 0);
     else
diff --git a/libc/test/src/ctype/iscntrl_test.cpp b/libc/test/src/ctype/iscntrl_test.cpp
--- a/libc/test/src/ctype/iscntrl_test.cpp
+++ b/libc/test/src/ctype/iscntrl_test.cpp
@@ -12,7 +12,7 @@
 TEST(LlvmLibcIsCntrl, DefaultLocale) {
   // Loops through all characters, verifying that control characters
   // return a non-zero integer, all others return zero.
-  for (int ch = 0; ch < 255; ++ch) {
+  for (int ch = -255; ch < 255; ++ch) {
     if ((0 <= ch && ch <= 0x1f /*US*/) || ch == 0x7f /*DEL*/)
       EXPECT_NE(__llvm_libc::iscntrl(ch), 0);
     else
diff --git a/libc/test/src/ctype/isdigit_test.cpp b/libc/test/src/ctype/isdigit_test.cpp
--- a/libc/test/src/ctype/isdigit_test.cpp
+++ b/libc/test/src/ctype/isdigit_test.cpp
@@ -13,7 +13,7 @@
 TEST(LlvmLibcIsDigit, DefaultLocale) {
   // Loops through all characters, verifying that numbers return a
   // non-zero integer and everything else returns zero.
-  for (int ch = 0; ch < 255; ++ch) {
+  for (int ch = -255; ch < 255; ++ch) {
     if ('0' <= ch && ch <= '9')
       EXPECT_NE(__llvm_libc::isdigit(ch), 0);
     else
diff --git a/libc/test/src/ctype/isgraph_test.cpp b/libc/test/src/ctype/isgraph_test.cpp
--- a/libc/test/src/ctype/isgraph_test.cpp
+++ b/libc/test/src/ctype/isgraph_test.cpp
@@ -12,7 +12,7 @@
 TEST(LlvmLibcIsGraph, DefaultLocale) {
   // Loops through all characters, verifying that graphical characters
   // return a non-zero integer, everything else returns zero.
-  for (int ch = 0; ch < 255; ++ch) {
+  for (int ch = -255; ch < 255; ++ch) {
     if ('!' <= ch && ch <= '~') // A-Z, a-z, 0-9, punctuation.
       EXPECT_NE(__llvm_libc::isgraph(ch), 0);
     else
diff --git a/libc/test/src/ctype/islower_test.cpp b/libc/test/src/ctype/islower_test.cpp
--- a/libc/test/src/ctype/islower_test.cpp
+++ b/libc/test/src/ctype/islower_test.cpp
@@ -12,7 +12,7 @@
 TEST(LlvmLibcIsLower, DefaultLocale) {
   // Loops through all characters, verifying that lowercase letters
   // return a non-zero integer and everything else returns zero.
-  for (int ch = 0; ch < 255; ++ch) {
+  for (int ch = -255; ch < 255; ++ch) {
     if ('a' <= ch && ch <= 'z')
       EXPECT_NE(__llvm_libc::islower(ch), 0);
     else
diff --git a/libc/test/src/ctype/isprint_test.cpp b/libc/test/src/ctype/isprint_test.cpp
--- a/libc/test/src/ctype/isprint_test.cpp
+++ b/libc/test/src/ctype/isprint_test.cpp
@@ -10,7 +10,7 @@
 #include "test/UnitTest/Test.h"
 
 TEST(LlvmLibcIsPrint, DefaultLocale) {
-  for (int ch = 0; ch < 255; ++ch) {
+  for (int ch = -255; ch < 255; ++ch) {
     if (' ' <= ch && ch <= '~') // A-Z, a-z, 0-9, punctuation, space.
       EXPECT_NE(__llvm_libc::isprint(ch), 0);
     else
diff --git a/libc/test/src/ctype/ispunct_test.cpp b/libc/test/src/ctype/ispunct_test.cpp
--- a/libc/test/src/ctype/ispunct_test.cpp
+++ b/libc/test/src/ctype/ispunct_test.cpp
@@ -25,7 +25,7 @@
 TEST(LlvmLibcIsPunct, DefaultLocale) {
   // Loops through all characters, verifying that punctuation characters
   // return a non-zero integer, and everything else returns zero.
-  for (int ch = 0; ch < 255; ++ch) {
+  for (int ch = -255; ch < 255; ++ch) {
     if (is_punctuation_character(ch))
       EXPECT_NE(__llvm_libc::ispunct(ch), 0);
     else
diff --git a/libc/test/src/ctype/isspace_test.cpp b/libc/test/src/ctype/isspace_test.cpp
--- a/libc/test/src/ctype/isspace_test.cpp
+++ b/libc/test/src/ctype/isspace_test.cpp
@@ -19,7 +19,7 @@
   //    0x0b     |   vertical tab
   //    0x0d     |   carriage return
   //    0x20     |   space
-  for (int ch = 0; ch < 255; ++ch) {
+  for (int ch = -255; ch < 255; ++ch) {
     if (ch == 0x20 || (0x09 <= ch && ch <= 0x0d))
       EXPECT_NE(__llvm_libc::isspace(ch), 0);
     else
diff --git a/libc/test/src/ctype/isupper_test.cpp b/libc/test/src/ctype/isupper_test.cpp
--- a/libc/test/src/ctype/isupper_test.cpp
+++ b/libc/test/src/ctype/isupper_test.cpp
@@ -12,7 +12,7 @@
 TEST(LlvmLibcIsUpper, DefaultLocale) {
   // Loops through all characters, verifying that uppercase letters
   // return a non-zero integer and everything else returns zero.
-  for (int ch = 0; ch < 255; ++ch) {
+  for (int ch = -255; ch < 255; ++ch) {
     if ('A' <= ch && ch <= 'Z')
       EXPECT_NE(__llvm_libc::isupper(ch), 0);
     else
diff --git a/libc/test/src/ctype/isxdigit_test.cpp b/libc/test/src/ctype/isxdigit_test.cpp
--- a/libc/test/src/ctype/isxdigit_test.cpp
+++ b/libc/test/src/ctype/isxdigit_test.cpp
@@ -10,7 +10,7 @@
 #include "test/UnitTest/Test.h"
 
 TEST(LlvmLibcIsXDigit, DefaultLocale) {
-  for (int ch = 0; ch < 255; ++ch) {
+  for (int ch = -255; ch < 255; ++ch) {
     if (('0' <= ch && ch <= '9') || ('a' <= ch && ch <= 'f') ||
         ('A' <= ch && ch <= 'F'))
       EXPECT_NE(__llvm_libc::isxdigit(ch), 0);
diff --git a/libc/test/src/ctype/toascii_test.cpp b/libc/test/src/ctype/toascii_test.cpp
--- a/libc/test/src/ctype/toascii_test.cpp
+++ b/libc/test/src/ctype/toascii_test.cpp
@@ -15,8 +15,8 @@
   //    (which are all 7 bit unsigned integers)
   // return themself, and that all other characters return themself
   // mod 128 (which is equivalent to & 0x7f)
-  for (int ch = 0; ch < 255; ++ch) {
-    if (ch <= 0x7f)
+  for (int ch = -255; ch < 255; ++ch) {
+    if (0 <= ch && ch <= 0x7f)
       EXPECT_EQ(__llvm_libc::toascii(ch), ch);
     else
       EXPECT_EQ(__llvm_libc::toascii(ch), ch & 0x7f);
diff --git a/libc/test/src/ctype/tolower_test.cpp b/libc/test/src/ctype/tolower_test.cpp
--- a/libc/test/src/ctype/tolower_test.cpp
+++ b/libc/test/src/ctype/tolower_test.cpp
@@ -10,7 +10,7 @@
 #include "test/UnitTest/Test.h"
 
 TEST(LlvmLibcToLower, DefaultLocale) {
-  for (int ch = 0; ch < 255; ++ch) {
+  for (int ch = -255; ch < 255; ++ch) {
     // This follows pattern 'A' + 32 = 'a'.
     if ('A' <= ch && ch <= 'Z')
       EXPECT_EQ(__llvm_libc::tolower(ch), ch + 32);
diff --git a/libc/test/src/ctype/toupper_test.cpp b/libc/test/src/ctype/toupper_test.cpp
--- a/libc/test/src/ctype/toupper_test.cpp
+++ b/libc/test/src/ctype/toupper_test.cpp
@@ -10,7 +10,7 @@
 #include "test/UnitTest/Test.h"
 
 TEST(LlvmLibcToUpper, DefaultLocale) {
-  for (int ch = 0; ch < 255; ++ch) {
+  for (int ch = -255; ch < 255; ++ch) {
     // This follows pattern 'a' - 32 = 'A'.
     if ('a' <= ch && ch <= 'z')
       EXPECT_EQ(__llvm_libc::toupper(ch), ch - 32);