diff --git a/src/V3Graph.cpp b/src/V3Graph.cpp
index dda271082..8a57523c3 100644
--- a/src/V3Graph.cpp
+++ b/src/V3Graph.cpp
@@ -274,18 +274,18 @@ void V3Graph::dumpEdge(ostream& os, V3GraphVertex* vertexp, V3GraphEdge* edgep)
     }
 }
 
-void V3Graph::dumpDotFilePrefixed(const string& nameComment, bool colorAsSubgraph) {
+void V3Graph::dumpDotFilePrefixed(const string& nameComment, bool colorAsSubgraph) const {
     if (v3Global.opt.dumpTree()) {
 	dumpDotFile(v3Global.debugFilename(nameComment)+".dot", colorAsSubgraph);
     }
 }
 
 //! Variant of dumpDotFilePrefixed without --dump option check
-void V3Graph::dumpDotFilePrefixedAlways(const string& nameComment, bool colorAsSubgraph) {
+void V3Graph::dumpDotFilePrefixedAlways(const string& nameComment, bool colorAsSubgraph) const {
     dumpDotFile(v3Global.debugFilename(nameComment)+".dot", colorAsSubgraph);
 }
 
-void V3Graph::dumpDotFile(const string& filename, bool colorAsSubgraph) {
+void V3Graph::dumpDotFile(const string& filename, bool colorAsSubgraph) const {
     // This generates a file used by graphviz, http://www.graphviz.org
     // "hardcoded" parameters:
     const vl_unique_ptr<ofstream> logp (V3File::new_ofstream(filename));
diff --git a/src/V3Graph.h b/src/V3Graph.h
index 221f8a428..b546f2d8e 100644
--- a/src/V3Graph.h
+++ b/src/V3Graph.h
@@ -65,7 +65,7 @@ public:
     V3Graph();
     virtual ~V3Graph();
     static void debug(int level) { s_debug = level; }
-    virtual string dotRankDir() { return "TB"; }	// rankdir for dot plotting
+    virtual string dotRankDir() const { return "TB"; }	// rankdir for dot plotting
 
     // METHODS
     void clear();	// Empty it of all vertices/edges, as if making a new object
@@ -127,9 +127,9 @@ public:
 
     /// Debugging
     void dump(ostream& os=cout);
-    void dumpDotFile(const string& filename, bool colorAsSubgraph);
-    void dumpDotFilePrefixed(const string& nameComment, bool colorAsSubgraph=false);
-    void dumpDotFilePrefixedAlways(const string& nameComment, bool colorAsSubgraph=false);
+    void dumpDotFile(const string& filename, bool colorAsSubgraph) const;
+    void dumpDotFilePrefixed(const string& nameComment, bool colorAsSubgraph=false) const;
+    void dumpDotFilePrefixedAlways(const string& nameComment, bool colorAsSubgraph=false) const;
     void userClearVertices();
     void userClearEdges();
     static void test();