diff --git a/tests/Makefile b/tests/Makefile
index c60374bf..66ce4277 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -166,8 +166,8 @@ gene-serial:
 #####################################################################################################
 
 coverage:
-	$(MAKE) `ls test-*.c|$(SED) 's/\.c/\.gcov/g'`
-	$(MAKE) synthesis
+	$(MAKE) `ls test-*.c|$(SED) 's/\.c/\.gcov/g'` CC="cc -std=c11"
+	$(MAKE) synthesis.synt check-synthesis
 
 SYNTHESIS_DATA=	M-ALGO test-malgo.c.c test-malgo.synt			\
 		M-ARRAY test-marray.c.c test-marray.synt				\
@@ -197,7 +197,7 @@ SYNTHESIS_DATA=	M-ALGO test-malgo.c.c test-malgo.synt			\
 		M-VARIANT test-mvariant.c.c test-mvariant.synt 			\
 		M-WORKER ../m-worker.h test-mworker.synt		
 
-synthesis:
+synthesis.synt:
 	@printf "+-------------------------------+-------------------------------+\n"
 	@for i in $(SYNTHESIS_DATA) ; do 							\
 	if test "$$j" = "" ; then j=$$i ; continue ; fi;			\
@@ -205,9 +205,14 @@ synthesis:
 	printf "|\t%16.16s\t|\t%16.16s\t|\n"	"$$j"	"`grep -v Creating $$i|grep $$k -F -A1 |tail -1|cut -f2 -d':'`"; 	\
 	j="";														\
 	k="";														\
-	done
+	done                                                        > synthesis.synt
+	@cat synthesis.synt
 	@printf "+-------------------------------+-------------------------------+\n"
 
+# Compare the computed coverage against the reference coverage (synthesis.ref), allowing only increase of coverage
+check-synthesis: synthesis.synt
+	@paste synthesis.ref synthesis.synt |awk '($$2 != $$9) {err=1} { n1=$$4*$$6/100 ; n2=$$11*$$13/100; if (n1 > n2) { printf "ERROR for %s: new coverage (%d) is lower than reference (%d)\n",$$2,n2,n1 ; err=2 } } END {exit err}'
+
 
 #####################################################################################################
 # Code analyzer tools
diff --git a/tests/synthesis.ref b/tests/synthesis.ref
new file mode 100644
index 00000000..9e2d20a7
--- /dev/null
+++ b/tests/synthesis.ref
@@ -0,0 +1,27 @@
+|	          M-ALGO	|	 100.00% of 1160	|
+|	         M-ARRAY	|	   98.24% of 908	|
+|	        M-BITSET	|	   98.31% of 413	|
+|	       M-BBPTREE	|	   99.60% of 998	|
+|	        M-BUFFER	|	   98.86% of 877	|
+|	    M-CONCURRENT	|	  100.00% of 102	|
+|	          M-CORE	|	  100.00% of 268	|
+|	         M-DEQUE	|	   99.47% of 943	|
+|	          M-DICT	|	  93.00% of 1528	|
+|	       M-FUNCOBJ	|	  100.00% of 108	|
+|	        M-GENINT	|	    97.40% of 77	|
+|	        M-I-LIST	|	   98.10% of 474	|
+|	      M-I-SHARED	|	   100.00% of 112	|
+|	          M-LIST	|	  99.12% of 1368	|
+|	       M-MEMPOOL	|	    97.98% of 99	|
+|	         M-MUTEX	|	   100.00% of 19	|
+|	     M-PRIOQUEUE	|	   99.17% of 600	|
+|	        M-RBTREE	|	   99.04% of 937	|
+|	    M-SERIAL-BIN	|	   70.87% of 254	|
+|	   M-SERIAL-JSON	|	  100.00% of 494	|
+|	        M-SHARED	|	   99.07% of 324	|
+|	      M-SNAPSHOT	|	   99.54% of 439	|
+|	        M-STRING	|	   99.40% of 831	|
+|	          M-TREE	|	  98.46% of 1232	|
+|	         M-TUPLE	|	  100.00% of 186	|
+|	       M-VARIANT	|	   99.25% of 266	|
+|	        M-WORKER	|	    98.73% of 79	|