diff --git a/mongoose.c b/mongoose.c
index 23ed3362..1406453c 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -4195,11 +4195,12 @@ int mg_asprintf(char **buf, size_t size, const char *fmt, ...) {
 }
 
 int64_t mg_to64(struct mg_str str) {
-  int64_t result = 0, neg = 1;
+  int64_t result = 0, neg = 1, max = 922337203685477580 /* INT64_MAX / 10 */;
   size_t i = 0;
   while (i < str.len && (str.ptr[i] == ' ' || str.ptr[i] == '\t')) i++;
   if (i < str.len && str.ptr[i] == '-') neg = -1, i++;
   while (i < str.len && str.ptr[i] >= '0' && str.ptr[i] <= '9') {
+    if (result > max) return 0;
     result *= 10;
     result += (str.ptr[i] - '0');
     i++;
diff --git a/src/util.c b/src/util.c
index 2943df73..d4f6c258 100644
--- a/src/util.c
+++ b/src/util.c
@@ -262,11 +262,12 @@ int mg_asprintf(char **buf, size_t size, const char *fmt, ...) {
 }
 
 int64_t mg_to64(struct mg_str str) {
-  int64_t result = 0, neg = 1;
+  int64_t result = 0, neg = 1, max = 922337203685477580 /* INT64_MAX / 10 */;
   size_t i = 0;
   while (i < str.len && (str.ptr[i] == ' ' || str.ptr[i] == '\t')) i++;
   if (i < str.len && str.ptr[i] == '-') neg = -1, i++;
   while (i < str.len && str.ptr[i] >= '0' && str.ptr[i] <= '9') {
+    if (result > max) return 0;
     result *= 10;
     result += (str.ptr[i] - '0');
     i++;