diff --git a/libc/src/string/memchr.cpp b/libc/src/string/memchr.cpp
--- a/libc/src/string/memchr.cpp
+++ b/libc/src/string/memchr.cpp
@@ -17,7 +17,8 @@
 // TODO: Look at performance benefits of comparing words.
 LLVM_LIBC_FUNCTION(void *, memchr, (const void *src, int c, size_t n)) {
   return internal::find_first_character(
-      reinterpret_cast<const unsigned char *>(src), c, n);
+      reinterpret_cast<const unsigned char *>(src),
+      static_cast<unsigned char>(c), n);
 }
 
 } // namespace __llvm_libc
diff --git a/libc/src/string/memory_utils/elements_x86.h b/libc/src/string/memory_utils/elements_x86.h
--- a/libc/src/string/memory_utils/elements_x86.h
+++ b/libc/src/string/memory_utils/elements_x86.h
@@ -67,7 +67,8 @@
   using T = char __attribute__((__vector_size__(SIZE)));
   static uint16_t mask(T value) {
     // NOLINTNEXTLINE(llvmlibc-callee-namespace)
-    return _mm_movemask_epi8(__llvm_libc::bit_cast<__m128i>(value));
+    return static_cast<uint16_t>(
+        _mm_movemask_epi8(__llvm_libc::bit_cast<__m128i>(value)));
   }
   static uint16_t not_equal_mask(T a, T b) { return mask(a != b); }
   static T load(const char *ptr) {
diff --git a/libc/src/string/memrchr.cpp b/libc/src/string/memrchr.cpp
--- a/libc/src/string/memrchr.cpp
+++ b/libc/src/string/memrchr.cpp
@@ -14,7 +14,7 @@
 
 LLVM_LIBC_FUNCTION(void *, memrchr, (const void *src, int c, size_t n)) {
   const unsigned char *str = reinterpret_cast<const unsigned char *>(src);
-  const unsigned char ch = c;
+  const unsigned char ch = static_cast<unsigned char>(c);
   for (; n != 0; --n) {
     const unsigned char *s = str + n - 1;
     if (*s == ch)
diff --git a/libc/src/string/strchr.cpp b/libc/src/string/strchr.cpp
--- a/libc/src/string/strchr.cpp
+++ b/libc/src/string/strchr.cpp
@@ -14,7 +14,7 @@
 
 // TODO: Look at performance benefits of comparing words.
 LLVM_LIBC_FUNCTION(char *, strchr, (const char *src, int c)) {
-  const char ch = c;
+  const char ch = static_cast<char>(c);
   for (; *src && *src != ch; ++src)
     ;
   return *src == ch ? const_cast<char *>(src) : nullptr;
diff --git a/libc/src/string/strrchr.cpp b/libc/src/string/strrchr.cpp
--- a/libc/src/string/strrchr.cpp
+++ b/libc/src/string/strrchr.cpp
@@ -13,7 +13,7 @@
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(char *, strrchr, (const char *src, int c)) {
-  const char ch = c;
+  const char ch = static_cast<char>(c);
   char *last_occurrence = nullptr;
   for (; *src; ++src) {
     if (*src == ch)