diff --git a/contrib/gen_html/Makefile b/contrib/gen_html/Makefile
index c68e560a1..ea68b11fc 100644
--- a/contrib/gen_html/Makefile
+++ b/contrib/gen_html/Makefile
@@ -7,12 +7,18 @@
 # of patent rights can be found in the PATENTS file in the same directory.
 # ##########################################################################
 
-
 CFLAGS ?= -O3
 CFLAGS += -Wall -Wextra -Wcast-qual -Wcast-align -Wshadow -Wstrict-aliasing=1 -Wswitch-enum -Wno-comment
 CFLAGS += $(MOREFLAGS)
-FLAGS   = $(CPPFLAGS) $(CFLAGS) $(LDFLAGS)
+FLAGS   = $(CPPFLAGS) $(CFLAGS) $(CXXFLAGS) $(LDFLAGS)
 
+ZSTDAPI = ../../lib/zstd.h
+ZSTDMANUAL = ../../doc/zstd_manual.html
+LIBVER_MAJOR_SCRIPT:=`sed -n '/define ZSTD_VERSION_MAJOR/s/.*[[:blank:]]\([0-9][0-9]*\).*/\1/p' < $(ZSTDAPI)`
+LIBVER_MINOR_SCRIPT:=`sed -n '/define ZSTD_VERSION_MINOR/s/.*[[:blank:]]\([0-9][0-9]*\).*/\1/p' < $(ZSTDAPI)`
+LIBVER_PATCH_SCRIPT:=`sed -n '/define ZSTD_VERSION_RELEASE/s/.*[[:blank:]]\([0-9][0-9]*\).*/\1/p' < $(ZSTDAPI)`
+LIBVER_SCRIPT:= $(LIBVER_MAJOR_SCRIPT).$(LIBVER_MINOR_SCRIPT).$(LIBVER_PATCH_SCRIPT)
+LIBVER := $(shell echo $(LIBVER_SCRIPT))
 
 
 # Define *.exe as extension for Windows systems
@@ -23,14 +29,23 @@ EXT =
 endif
 
 
-.PHONY: default gen_html
-
+.PHONY: default
 default: gen_html
 
+.PHONY: all
+all: manual
+
 gen_html: gen_html.cpp
-	$(CXX)      $(FLAGS) $^ -o $@$(EXT)
+	$(CXX) $(FLAGS) $^ -o $@$(EXT)
 
+$(ZSTDMANUAL): gen_html $(ZSTDAPI)
+	echo "Update zstd manual in /doc"
+	./gen_html $(LIBVER) $(ZSTDAPI) $(ZSTDMANUAL)
 
+.PHONY: manual
+manual: gen_html $(ZSTDMANUAL)
+
+.PHONY: clean
 clean:
 	@$(RM) gen_html$(EXT)
 	@echo Cleaning completed