diff --git a/pppd/Makefile.linux b/pppd/Makefile.linux
index 060db6a..c151c62 100644
--- a/pppd/Makefile.linux
+++ b/pppd/Makefile.linux
@@ -117,7 +117,7 @@ CFLAGS   += -DHAS_SHADOW
 #LIBS     += -lshadow $(LIBS)
 endif
 
-ifneq ($(wildcard /usr/include/crypt.h),)
+ifneq ($(wildcard @glibc@/include/crypt.h),)
 CFLAGS  += -DHAVE_CRYPT_H=1
 LIBS	+= -lcrypt
 endif
@@ -169,7 +169,7 @@ LIBS	+= -ldl
 endif
 
 ifdef FILTER
-ifneq ($(wildcard /usr/include/pcap-bpf.h),)
+ifneq ($(wildcard @libpcap@/include/pcap-bpf.h),)
 LIBS    += -lpcap
 CFLAGS  += -DPPP_FILTER
 endif
