diff --git a/dtool/src/dtoolbase/p3dtoolbase_composite2.cxx b/dtool/src/dtoolbase/p3dtoolbase_composite2.cxx
index 145c86d801..8cd964b4fd 100644
--- a/dtool/src/dtoolbase/p3dtoolbase_composite2.cxx
+++ b/dtool/src/dtoolbase/p3dtoolbase_composite2.cxx
@@ -2,7 +2,7 @@
 #include "mutexWin32Impl.cxx"
 #include "mutexSpinlockImpl.cxx"
 #include "neverFreeMemory.cxx"
-#include "pdtoa.c"
+#include "pdtoa.cxx"
 #include "pstrtod.cxx"
 #include "register_type.cxx"
 #include "typeHandle.cxx"
diff --git a/dtool/src/dtoolbase/pdtoa.c b/dtool/src/dtoolbase/pdtoa.cxx
similarity index 100%
rename from dtool/src/dtoolbase/pdtoa.c
rename to dtool/src/dtoolbase/pdtoa.cxx