diff --git a/src/http.c b/src/http.c
index 703c58caa..c04c58500 100644
--- a/src/http.c
+++ b/src/http.c
@@ -272,16 +272,17 @@ static void _http_add_body_bytes(tf_http_connection_t* connection, const void* d
 				}
 				mask_start = 10;
 			}
-			if (connection->body_length >= mask_start + length + 4)
+			size_t total_length = mask_start + 4 + length;
+			if (connection->body_length >= total_length)
 			{
 				uint32_t mask =
 					(uint32_t)p[mask_start + 0] |
 					(uint32_t)p[mask_start + 1] << 8 |
 					(uint32_t)p[mask_start + 2] << 16 |
 					(uint32_t)p[mask_start + 3] << 24;
-				_http_websocket_mask_in_place(p + mask_start + 4, mask, length);
+				uint8_t* message = p + mask_start + 4;
+				_http_websocket_mask_in_place(message, mask, length);
 
-				const uint8_t* message = p + mask_start + 4;
 				if (!fin && !connection->fragment_op_code)
 				{
 					connection->fragment_op_code = op_code;
@@ -307,9 +308,11 @@ static void _http_add_body_bytes(tf_http_connection_t* connection, const void* d
 					connection->fragment_length = 0;
 				}
 				connection->websocket_message_index++;
-				size_t total_length = mask_start + 4 + length;
-				memmove(connection->body, (char*)connection->body + total_length, connection->body_length - total_length);
-				connection->body_length -= total_length;
+				if (connection->body_length > total_length)
+				{
+					memmove(connection->body, (char*)connection->body + total_length, connection->body_length - total_length);
+					connection->body_length -= total_length;
+				}
 			}
 			else
 			{