diff --git a/libc/src/__support/common.h b/libc/src/__support/common.h
--- a/libc/src/__support/common.h
+++ b/libc/src/__support/common.h
@@ -15,6 +15,18 @@
 #define unlikely(x) __builtin_expect(x, 0)
 #define UNUSED __attribute__((unused))
 
+#ifdef __has_attribute
+#define LIBC_HAVE_ATTRIBUTE(x) __has_attribute(x)
+#else
+#define LIBC_HAVE_ATTRIBUTE(x) 0
+#endif
+
+#if LIBC_HAVE_ATTRIBUTE(aligned) || (defined(__GNUC__) && !defined(__clang__))
+#define LIBC_ATTRIBUTE_FUNC_ALIGN(bytes) __attribute__((aligned(bytes)))
+#else
+#define LIBC_ATTRIBUTE_FUNC_ALIGN(bytes)
+#endif
+
 #ifndef LLVM_LIBC_FUNCTION_ATTR
 #define LLVM_LIBC_FUNCTION_ATTR
 #endif
@@ -25,9 +37,10 @@
   LLVM_LIBC_FUNCTION_ATTR decltype(__llvm_libc::name)                          \
       __##name##_impl__ __asm__(#name);                                        \
   decltype(__llvm_libc::name) name [[gnu::alias(#name)]];                      \
-  type __##name##_impl__ arglist
+  type LIBC_ATTRIBUTE_FUNC_ALIGN(64) __##name##_impl__ arglist
 #else
-#define LLVM_LIBC_FUNCTION(type, name, arglist) type name arglist
+#define LLVM_LIBC_FUNCTION(type, name, arglist)                                \
+  type LIBC_ATTRIBUTE_FUNC_ALIGN(64) name arglist
 #endif
 
 namespace __llvm_libc {