diff --git a/Makefile b/Makefile
index 1f4960eab161deaba6f57ac902fd073b2119739a..922a516856b78c1531966abb2a2698d040681be1 100644
--- a/Makefile
+++ b/Makefile
@@ -2,6 +2,9 @@ include $(FSLCONFDIR)/default.mk
 
 PROJNAME = siena
 
+USRINCFLAGS = -I${INC_ZLIB}
+USRLDFLAGS = -L${LIB_ZLIB}
+
 LIBS = -lss_32R -lfslio -lniftiio -lznz -lm -lz
 
 XFILES = siena_diff