diff --git a/src/ca/legacy/gdd/Makefile b/src/ca/legacy/gdd/Makefile
index 9c5638eb4..335d49001 100644
--- a/src/ca/legacy/gdd/Makefile
+++ b/src/ca/legacy/gdd/Makefile
@@ -68,6 +68,7 @@ CLEANS += $(COMMON_DIR)/aitConvertGenerated.cc
 
 USR_CXXFLAGS_Linux = -fno-strict-aliasing
 USR_CXXFLAGS_RTEMS = -fno-strict-aliasing
+USR_CXXFLAGS_vxWorks = -fno-strict-aliasing
 
 ifeq ($(T_A),$(EPICS_HOST_ARCH))
   # genApps and aitGen are needed to finish libgdd
diff --git a/src/ca/legacy/pcas/build/Makefile b/src/ca/legacy/pcas/build/Makefile
index e30560882..b4783fc17 100644
--- a/src/ca/legacy/pcas/build/Makefile
+++ b/src/ca/legacy/pcas/build/Makefile
@@ -72,6 +72,10 @@ LIBSRCS += casDGIntfIO.cc
 LIBSRCS += casStreamIO.cc
 LIBSRCS += ipIgnoreEntry.cc
 
+USR_CXXFLAGS_Linux = -fno-strict-aliasing
+USR_CXXFLAGS_RTEMS = -fno-strict-aliasing
+USR_CXXFLAGS_vxWorks = -fno-strict-aliasing
+
 # There is a bug in some vxWorks compilers that these work around:
 ifeq ($(VX_GNU_VERSION), 4.1.2)
   casStreamOS_CXXFLAGS_vxWorks-ppc604_altivec = -O0