diff --git a/examples/embedded_c/embedded_c.c b/examples/embedded_c/embedded_c.c
index 4ff22433..33511ce8 100644
--- a/examples/embedded_c/embedded_c.c
+++ b/examples/embedded_c/embedded_c.c
@@ -231,7 +231,7 @@ field_get(const char *key, const char *value, size_t valuelen, void *user_data)
 
 
 int
-field_stored(const char *path, size_t file_size, void *user_data)
+field_stored(const char *path, long long file_size, void *user_data)
 {
 	struct mg_connection *conn = (struct mg_connection *)user_data;
 
diff --git a/include/civetweb.h b/include/civetweb.h
index f4ad376a..97029856 100644
--- a/include/civetweb.h
+++ b/include/civetweb.h
@@ -814,7 +814,7 @@ struct mg_form_data_handler {
 	 * Return value:
 	 *   TODO: Needs to be defined.
 	 */
-	int (*field_store)(const char *path, size_t file_size, void *user_data);
+	int (*field_store)(const char *path, long long file_size, void *user_data);
 
 	/* User supplied argument, passed to all callback functions. */
 	void *user_data;
diff --git a/src/civetweb.c b/src/civetweb.c
index bb349308..98130f53 100644
--- a/src/civetweb.c
+++ b/src/civetweb.c
@@ -9319,7 +9319,7 @@ mg_upload_field_get(const char *key,
 
 /* Helper function for deprecated mg_upload. */
 static int
-mg_upload_field_stored(const char *path, size_t file_size, void *user_data)
+mg_upload_field_stored(const char *path, long long file_size, void *user_data)
 {
 	struct mg_upload_user_data *fud = (struct mg_upload_user_data *)user_data;
 	(void)file_size;
diff --git a/src/handle_form.inl b/src/handle_form.inl
index 82a8ebcd..4e6b28b9 100644
--- a/src/handle_form.inl
+++ b/src/handle_form.inl
@@ -117,7 +117,7 @@ url_encoded_field_get(const struct mg_connection *conn,
 static int
 field_stored(const struct mg_connection *conn,
              const char *path,
-             size_t file_size,
+             long long file_size,
              struct mg_form_data_handler *fdh)
 {
 	/* Equivalent to "upload" callback of "mg_upload". */
@@ -162,7 +162,7 @@ mg_handle_form_request(struct mg_connection *conn,
 	int r;
 	int field_count = 0;
 	struct file fstore = STRUCT_FILE_INITIALIZER;
-	size_t file_size = 0; /* init here, to a avoid a false positive
+	int64_t file_size = 0; /* init here, to a avoid a false positive
 	                         "uninitialized variable used" warning */
 
 	int has_body_data =