diff --git a/kdbg/testprogs/Makefile.am b/kdbg/testprogs/Makefile.am
index ba751b2..a59a6ce 100644
--- a/kdbg/testprogs/Makefile.am
+++ b/kdbg/testprogs/Makefile.am
@@ -8,7 +8,7 @@ AM_CXXFLAGS = -g
 
 # Disable optimization to ensure that variables are not hidden by the
 # compiler
-CXXFLAGS = $(patsubst -O%,,$(CXXFLAGS))
+CXXFLAGS := $(patsubst -O%,,$(CXXFLAGS))
 
 if BUILDTESTPROGS
 PROGS = \