diff --git a/ext/ffi/php_ffi.h b/ext/ffi/php_ffi.h
index fc6120de7981f..3a10b45478c2a 100644
--- a/ext/ffi/php_ffi.h
+++ b/ext/ffi/php_ffi.h
@@ -198,7 +198,7 @@ typedef struct _zend_ffi_val {
 		uint64_t        u64;
 		int64_t         i64;
 		zend_ffi_double d;
-		char            ch;
+		signed char     ch;
 		struct {
 			const char *str;
 			size_t      len;