diff --git a/App/tools/driver.makefile b/App/tools/driver.makefile
index a13504d27558bca3775fa72b9eff20ab302b92c0..423e5e4de8b12f337a90cd422e0af6d291378bf7 100644
--- a/App/tools/driver.makefile
+++ b/App/tools/driver.makefile
@@ -679,7 +679,7 @@ DBDEXPANDPATH = $(addprefix -I , ${DBD_PATH} ${EPICS_BASE}/dbd)
 USR_DBDFLAGS += $(DBDEXPANDPATH)
 
 # search all directories where sources or headers come from, plus existing os dependend subdirectories
-SRC_INCLUDES = $(addprefix -I, $(wildcard $(foreach d,$(call uniq, $(filter-out /%,$(dir ${SRCS:%=../%} ${HDRS:%=../%}))), $d $d/os/${OS_CLASS} $d/os/default)))
+SRC_INCLUDES = $(addprefix -I, $(wildcard $(foreach d,$(call uniq, $(filter-out /%,$(dir ${SRCS:%=../%} ${HDRS:%=../%}))), $d $(addprefix $d/, os/${OS_CLASS} $(POSIX_$(POSIX)) os/default))))
 
 # different macro name for 3.14.8
 GENERIC_SRC_INCLUDES = $(SRC_INCLUDES)