diff --git a/ext/zlib/zlib.c b/ext/zlib/zlib.c
index 1ed5d06dac8..cb8db9b0a97 100644
--- a/ext/zlib/zlib.c
+++ b/ext/zlib/zlib.c
@@ -1171,8 +1171,7 @@ PHP_FUNCTION(deflate_add)
 		if (ctx->avail_out == 0) {
 			/* more output buffer space needed; realloc and try again */
 			/* adding 64 more bytes solved every issue I have seen    */
-			/* the + 1 is for the string terminator added below */
-			out = zend_string_realloc(out, ZSTR_LEN(out) + 64 + 1, 0);
+			out = zend_string_realloc(out, ZSTR_LEN(out) + 64, 0);
 			ctx->avail_out = 64;
 			ctx->next_out = (Bytef *) ZSTR_VAL(out) + buffer_used;
 		}