diff --git a/contrib/halog/Makefile b/contrib/halog/Makefile
index 26758e8..5e687c0 100644
--- a/contrib/halog/Makefile
+++ b/contrib/halog/Makefile
@@ -6,10 +6,17 @@
 # note: it is recommended to also add -fomit-frame-pointer on i386
 OPTIMIZE = -O3
 
+# most recent glibc provide platform-specific optimizations that make
+# memchr faster than the generic C implementation (eg: SSE and prefetch
+# on x86_64). Try with an without. In general, on x86_64 it's better to
+# use memchr using the define below.
+# DEFINE   = -DUSE_MEMCHR
+DEFINE   =
+
 OBJS     = halog
 
 halog: halog.c fgets2.c
-	$(CC) $(OPTIMIZE) -o $@ $(INCLUDE) $(EBTREE_DIR)/ebtree.c $(EBTREE_DIR)/eb32tree.c $(EBTREE_DIR)/eb64tree.c $(EBTREE_DIR)/ebmbtree.c $(EBTREE_DIR)/ebsttree.c $(EBTREE_DIR)/ebistree.c $(EBTREE_DIR)/ebimtree.c $^
+	$(CC) $(OPTIMIZE) $(DEFINE) -o $@ $(INCLUDE) $(EBTREE_DIR)/ebtree.c $(EBTREE_DIR)/eb32tree.c $(EBTREE_DIR)/eb64tree.c $(EBTREE_DIR)/ebmbtree.c $(EBTREE_DIR)/ebsttree.c $(EBTREE_DIR)/ebistree.c $(EBTREE_DIR)/ebimtree.c $^
 
 clean:
 	rm -f $(OBJS) *.[oas]