diff --git a/mongoose.c b/mongoose.c
index 6b258f5b..e946730f 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -4930,6 +4930,7 @@ const char *mg_strstr(const struct mg_str haystack,
                       const struct mg_str needle) {
   size_t i;
   if (needle.len > haystack.len) return NULL;
+  if (needle.len == 0) return haystack.ptr;
   for (i = 0; i <= haystack.len - needle.len; i++) {
     if (memcmp(haystack.ptr + i, needle.ptr, needle.len) == 0) {
       return haystack.ptr + i;
diff --git a/src/str.c b/src/str.c
index 329a067d..20af52e7 100644
--- a/src/str.c
+++ b/src/str.c
@@ -74,6 +74,7 @@ const char *mg_strstr(const struct mg_str haystack,
                       const struct mg_str needle) {
   size_t i;
   if (needle.len > haystack.len) return NULL;
+  if (needle.len == 0) return haystack.ptr;
   for (i = 0; i <= haystack.len - needle.len; i++) {
     if (memcmp(haystack.ptr + i, needle.ptr, needle.len) == 0) {
       return haystack.ptr + i;