diff --git a/diff-merges.c b/diff-merges.c
index 047bf81e67..eff54cca82 100644
--- a/diff-merges.c
+++ b/diff-merges.c
@@ -4,7 +4,7 @@
 
 static void suppress(struct rev_info *revs)
 {
-	revs->ignore_merges = 1;
+	revs->separate_merges = 0;
 	revs->first_parent_merges = 0;
 	revs->combine_merges = 0;
 	revs->dense_combined_merges = 0;
@@ -23,7 +23,6 @@ static void set_dense_combined(struct rev_info *revs)
 
 void diff_merges_init_revs(struct rev_info *revs)
 {
-	revs->ignore_merges = -1;
 }
 
 int diff_merges_parse_opts(struct rev_info *revs, const char **argv)
@@ -39,7 +38,7 @@ int diff_merges_parse_opts(struct rev_info *revs, const char **argv)
 		 * family of commands, it means "show full diff for merges". Set
 		 * both fields appropriately.
 		 */
-		revs->ignore_merges = 0;
+		revs->separate_merges = 1;
 		revs->match_missing = 1;
 	} else if (!strcmp(arg, "-c")) {
 		revs->dense_combined_merges = 0;
@@ -57,8 +56,9 @@ int diff_merges_parse_opts(struct rev_info *revs, const char **argv)
 			die(_("unknown value for --diff-merges: %s"), optarg);
 		}
 	} else
-		argcount = 0;
+		return 0;
 
+	revs->explicit_diff_merges = 1;
 	return argcount;
 }
 
@@ -69,21 +69,16 @@ void diff_merges_suppress(struct rev_info *revs)
 
 void diff_merges_default_to_first_parent(struct rev_info *revs)
 {
-	if (revs->ignore_merges < 0)		/* No -m */
-		revs->ignore_merges = 0;
-	if (!revs->combine_merges)		/* No -c/--cc" */
+	if (!revs->explicit_diff_merges)
+		revs->separate_merges = 1;
+	if (revs->separate_merges)
 		revs->first_parent_merges = 1;
 }
 
 void diff_merges_default_to_dense_combined(struct rev_info *revs)
 {
-	if (revs->ignore_merges < 0) {		/* No -m */
-		revs->ignore_merges = 0;
-		if (!revs->combine_merges) {	/* No -c/--cc" */
-			revs->combine_merges = 1;
-			revs->dense_combined_merges = 1;
-		}
-	}
+	if (!revs->explicit_diff_merges)
+		set_dense_combined(revs);
 }
 
 void diff_merges_set_dense_combined_if_unset(struct rev_info *revs)
@@ -94,10 +89,10 @@ void diff_merges_set_dense_combined_if_unset(struct rev_info *revs)
 
 void diff_merges_setup_revs(struct rev_info *revs)
 {
-	if (revs->combine_merges && revs->ignore_merges < 0)
-		revs->ignore_merges = 0;
-	if (revs->ignore_merges < 0)
-		revs->ignore_merges = 1;
+	if (revs->combine_merges == 0)
+		revs->dense_combined_merges = 0;
+	if (revs->separate_merges == 0)
+		revs->first_parent_merges = 0;
 	if (revs->combined_all_paths && !revs->combine_merges)
 		die("--combined-all-paths makes no sense without -c or --cc");
 	if (revs->combine_merges) {
diff --git a/log-tree.c b/log-tree.c
index 3fdc0fc64b..f9385b1dae 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -918,14 +918,15 @@ static int log_tree_diff(struct rev_info *opt, struct commit *commit, struct log
 
 	/* More than one parent? */
 	if (parents->next) {
-		if (opt->ignore_merges)
-			return 0;
-		else if (opt->combine_merges)
+		if (opt->combine_merges)
 			return do_diff_combined(opt, commit);
-		else if (!opt->first_parent_merges) {
-			/* If we show multiple diffs, show the parent info */
-			log->parent = parents->item;
-		}
+		if (opt->separate_merges) {
+			if (!opt->first_parent_merges) {
+				/* Show parent info for multiple diffs */
+				log->parent = parents->item;
+			}
+		} else
+			return 0;
 	}
 
 	showed_log = 0;
diff --git a/revision.h b/revision.h
index ba2aef7921..fcc532c873 100644
--- a/revision.h
+++ b/revision.h
@@ -191,12 +191,13 @@ struct rev_info {
 			match_missing:1,
 			no_commit_id:1,
 			verbose_header:1,
+			explicit_diff_merges: 1,
+			separate_merges: 1,
 			combine_merges:1,
 			combined_all_paths:1,
 			dense_combined_merges:1,
 			first_parent_merges:1,
 			always_show_header:1;
-	int             ignore_merges:2;
 
 	/* Format info */
 	int		show_notes;