diff --git a/config/CONFIG_COMMON b/config/CONFIG_COMMON
index 650d87989..a13180729 100644
--- a/config/CONFIG_COMMON
+++ b/config/CONFIG_COMMON
@@ -87,7 +87,7 @@ EPICS_BASE_BIN          = $(EPICS_BASE)/bin/$(T_A)
 GCC_ANSI = $(GCC) -ansi
 GCC_STRICT = $(GCC) -ansi -pedantic
 GCC_TRAD = $(GCC) -traditional
-GCC_DEP_CFLAGS = -fPIC -D_REENTRANT -D_POSIX_C_SOURCE=199506L -D_POSIX_THREADS
+GCC_DEP_CFLAGS = -fPIC -D_REENTRANT
 
 GCC_WARN_YES = -Wall
 GCC_WARN_NO = -w
@@ -104,7 +104,7 @@ G++_NORMAL = $(G++) -ansi -pedantic
 G++_STRICT = $(G++) -ansi -pedantic -Wtraditional
 G++_TRAD = $(G++) -traditional
 G++_TEMPL_INST_FLAG = -DEXPL_TEMPL
-G++_DEP_CFLAGS = -fPIC -D_REENTRANT -D_POSIX_C_SOURCE=199506L -D_POSIX_THREADS
+G++_DEP_CFLAGS = -fPIC -D_REENTRANT
 G++_WARN_YES = -Wall \
       -Wmissing-prototypes -Woverloaded-virtual \
       -Wwrite-strings -Wconversion -Wstrict-prototypes\
@@ -188,6 +188,15 @@ OS_CLASS = $(ARCH_CLASS)
 EPICS_INCLUDES = -I$(INSTALL_INCLUDE)/os/$(OS_CLASS) -I$(INSTALL_INCLUDE)
 EPICS_DBDFLAGS = -I $(INSTALL_LOCATION)/dbd
 
+#--------------------------------------------------
+# Posix flags
+POSIX=YES
+POSIX_CPPFLAGS_YES += -D_POSIX_C_SOURCE=199506L
+POSIX_LDLIBS_YES +=
+
+POSIX_CPPFLAGS += $(POSIX_CPPFLAGS_$(POSIX))
+POSIX_LDLIBS += $(POSIX_LDLIBS_$(POSIX))
+
 #--------------------------------------------------
 # Warnings flags  (CONFIG.Vx will override)
 WARN_CFLAGS = $($(ANSI)_WARN_$(HOST_WARN))
@@ -232,9 +241,9 @@ LDFLAGS = $(OPT_LDFLAGS) $(TARGET_LDFLAGS) $(USR_LDFLAGS)\
  $(ARCH_DEP_LDFLAGS) $(STATIC_LDFLAGS) $(OP_SYS_LDFLAGS)
 
 LDLIBS = $(TARGET_LDLIBS) $(USR_LDLIBS) $(ARCH_DEP_LDLIBS)\
- $(STATIC_LDLIBS) $(OP_SYS_LDLIBS)
+ $(STATIC_LDLIBS) $(OP_SYS_LDLIBS) $(POSIX_LDLIBS)
 
-CPPFLAGS += $(TARGET_CPPFLAGS) $(USR_CPPFLAGS) $(ARCH_DEP_CPPFLAGS)
+CPPFLAGS += $(TARGET_CPPFLAGS) $(USR_CPPFLAGS) $(ARCH_DEP_CPPFLAGS) $(POSIX_CPPFLAGS)
 
 CPPSNCFLAGS = $(INCLUDES)