diff --git a/src/core/ext/transport/chttp2/alpn/alpn.cc b/src/core/ext/transport/chttp2/alpn/alpn.cc
index 432f2c06076..be9c617a14f 100644
--- a/src/core/ext/transport/chttp2/alpn/alpn.cc
+++ b/src/core/ext/transport/chttp2/alpn/alpn.cc
@@ -30,7 +30,10 @@ static const char* const supported_versions[] = {"h2"};
 int grpc_chttp2_is_alpn_version_supported(const char* version, size_t size) {
   size_t i;
   for (i = 0; i < GPR_ARRAY_SIZE(supported_versions); i++) {
-    if (!strncmp(version, supported_versions[i], size)) return 1;
+    if (size == strlen(supported_versions[i]) &&
+        !strncmp(version, supported_versions[i], size)) {
+      return 1;
+    }
   }
   return 0;
 }