diff --git a/Core/Debugger/SymbolMap.cpp b/Core/Debugger/SymbolMap.cpp
index d11b99bc06..b2badb0b4c 100644
--- a/Core/Debugger/SymbolMap.cpp
+++ b/Core/Debugger/SymbolMap.cpp
@@ -422,7 +422,7 @@ struct Sig
 	{
 		strncpy(name,_name,63);
 	}
-	bool operator <(const Sig &other) {
+	bool operator <(const Sig &other) const {
 		return inst < other.inst;
 	}
 };