diff --git a/src/V3Fork.cpp b/src/V3Fork.cpp
index 6100c9cfd..2397b5037 100644
--- a/src/V3Fork.cpp
+++ b/src/V3Fork.cpp
@@ -270,8 +270,8 @@ private:
     int m_forkDepth = 0;  // Number of asynchronous forks we are currently under
     bool m_afterTimingControl = false;  // A timing control might've be executed in the current
                                         // process
-    size_t m_id;  // Unique ID for a frame
-    size_t m_class_id;  // Unique ID for a frame class
+    size_t m_id = 0;  // Unique ID for a frame
+    size_t m_class_id = 0;  // Unique ID for a frame class
 
     // METHODS