diff --git a/Makefile b/Makefile
index 3d629b10..76a3444e 100644
--- a/Makefile
+++ b/Makefile
@@ -11,12 +11,12 @@ all:	essai
 #---------------------------------------------------------------
 
 essai:		essai.c libfloatimg.a floatimg.h Makefile
-	gcc $(COPT) $< $(LDOPT) -lpnglite -o $@
+	gcc $(COPT) $< $(LDOPT) -lpnglite -lz -o $@
 
 #---------------------------------------------------------------
 
 TOTAR = *.[ch] Makefile *.sh *.txt 			\
-	doc/*.tex doc/mkdoc.sh				\
+	doc/*.tex doc/mkdoc.sh	doc/*.txt		\
 	funcs/*.[ch] funcs/Makefile			\
 	tools/*.[ch] tools/Makefile			\
 	v4l2/*.[ch] v4l2/Makefile			\
diff --git a/funcs/Makefile b/funcs/Makefile
index c631a7e1..55fa0feb 100644
--- a/funcs/Makefile
+++ b/funcs/Makefile
@@ -8,7 +8,7 @@ OBJS = fimg-png.o fimg-tiff.o misc-plots.o filtrage.o utils.o	\
 #---------------------------------------------------------------
 
 t:	t.c $(DEPS) ../libfloatimg.a
-	gcc $(COPT) $< ../libfloatimg.a -lnetpbm -lpnglite -lm -o $@
+	gcc $(COPT) $< ../libfloatimg.a -lnetpbm -lpnglite -lz -lm -o $@
 
 #---------------------------------------------------------------
 
diff --git a/lib/Makefile b/lib/Makefile
index 92bc1a55..83d026a5 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -16,7 +16,7 @@ AR=ar
 all:	$(OBJS) ../libfloatimg.a
 
 t:	t.c ../libfloatimg.a $(DEPS)
-	gcc $(COPT) $< ../libfloatimg.a -lpnglite -lm -o $@
+	gcc $(COPT) $< ../libfloatimg.a -lpnglite -lz -lm -o $@
 
 # --------------------------------------------
 
diff --git a/tools/Makefile b/tools/Makefile
index 088d54f3..bdf820a6 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -30,8 +30,12 @@ fimg2pnm:	fimg2pnm.c  $(DEPS)
 	gcc $(COPT) $< ../libfloatimg.a -o $@ 
 
 fimg2png:	fimg2png.c  $(DEPS)
-	gcc $(COPT) $< ../libfloatimg.a -lpnglite -o $@ 
+	gcc $(COPT) $< ../libfloatimg.a -lpnglite -lz -o $@ 
 
+#
+# this tool require an external library
+# http://la.buvette.org/devel/libimage/libimage.html
+#
 addtga2fimg:	addtga2fimg.c  $(DEPS)
 	gcc $(COPT) $< ../libfloatimg.a -limageSO -lm -o $@
 
@@ -41,5 +45,5 @@ addpnm2fimg:	addpnm2fimg.c  $(DEPS)
 
 # if "undefined reference to crc32" then "use -lz"
 png2fimg:	png2fimg.c  $(DEPS)
-	gcc $(COPT) $< ../libfloatimg.a -lpnglite -o $@
+	gcc $(COPT) $< ../libfloatimg.a -lpnglite -lz -o $@
 
diff --git a/v4l2/Makefile b/v4l2/Makefile
index 86cad481..e439bb23 100644
--- a/v4l2/Makefile
+++ b/v4l2/Makefile
@@ -18,7 +18,7 @@ v4l2_pr_structs.o:	v4l2_pr_structs.c v4l2_pr_structs.h Makefile
 	gcc ${COPT} -c $<
 
 grabvidseq: grabvidseq.c ${DEPS} rgb2fimg.o 
-	gcc ${COPT} $<  rgb2fimg.o ../libfloatimg.a -lm -lv4l2 -o $@
+	gcc ${COPT} $<  rgb2fimg.o ../libfloatimg.a -lz -lm -lv4l2 -o $@
 
 video-infos: video-infos.c Makefile funcs.o v4l2_pr_structs.o
 	gcc -Wall -g $<  funcs.o v4l2_pr_structs.o -o $@