diff --git a/ext/standard/base64.c b/ext/standard/base64.c
index 3893438839aee..82aa58a4b88ad 100644
--- a/ext/standard/base64.c
+++ b/ext/standard/base64.c
@@ -20,6 +20,10 @@
 #include "php.h"
 #include "base64.h"
 
+#if __has_feature(memory_sanitizer)
+# include <sanitizer/msan_interface.h>
+#endif
+
 /* {{{ base64 tables */
 static const char base64_table[] = {
 	'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
@@ -891,6 +895,12 @@ PHPAPI zend_string *php_base64_encode(const unsigned char *str, size_t length)
 	zend_string *result;
 
 	result = zend_string_safe_alloc(((length + 2) / 3), 4 * sizeof(char), 0, 0);
+
+#  if __has_feature(memory_sanitizer)
+		/* Clang 18 MSan does not instrument on AArch64. */
+		__msan_unpoison(ZSTR_VAL(result), ZSTR_LEN(result));
+#  endif
+
 	p = (unsigned char *)ZSTR_VAL(result);
 
 	p = php_base64_encode_impl(str, length, p);
@@ -913,6 +923,11 @@ PHPAPI zend_string *php_base64_decode_ex(const unsigned char *str, size_t length
 
 	result = zend_string_alloc(length, 0);
 
+#  if __has_feature(memory_sanitizer)
+		/* Clang 18 MSan does not instrument on AArch64. */
+		__msan_unpoison(ZSTR_VAL(result), ZSTR_LEN(result));
+#  endif
+
 	if (!php_base64_decode_impl(str, length, (unsigned char*)ZSTR_VAL(result), &outl, strict)) {
 		zend_string_efree(result);
 		return NULL;
diff --git a/ext/standard/basic_functions.c b/ext/standard/basic_functions.c
index 7bc7122b85963..f3a10d8c81d40 100755
--- a/ext/standard/basic_functions.c
+++ b/ext/standard/basic_functions.c
@@ -1190,7 +1190,7 @@ PHP_FUNCTION(usleep)
 PHP_FUNCTION(time_nanosleep)
 {
 	zend_long tv_sec, tv_nsec;
-	struct timespec php_req, php_rem;
+	struct timespec php_req, php_rem = {0};
 
 	ZEND_PARSE_PARAMETERS_START(2, 2)
 		Z_PARAM_LONG(tv_sec)