diff --git a/builtin-diff-files.c b/builtin-diff-files.c
index 9bf10bb37e..2b578c714d 100644
--- a/builtin-diff-files.c
+++ b/builtin-diff-files.c
@@ -50,7 +50,12 @@ int cmd_diff_files(int argc, const char **argv, const char *prefix)
 	    3 < rev.max_count)
 		usage(diff_files_usage);
 
-	if (rev.max_count == -1 &&
+	/*
+	 * "diff-files --base -p" should not combine merges because it
+	 * was not asked to.  "diff-files -c -p" should not densify
+	 * (the user should ask with "diff-files --cc" explicitly).
+	 */
+	if (rev.max_count == -1 && !rev.combine_merges &&
 	    (rev.diffopt.output_format & DIFF_FORMAT_PATCH))
 		rev.combine_merges = rev.dense_combined_merges = 1;
 
diff --git a/builtin-diff.c b/builtin-diff.c
index 037c3039a4..d5fe775fc1 100644
--- a/builtin-diff.c
+++ b/builtin-diff.c
@@ -223,7 +223,13 @@ static int builtin_diff_files(struct rev_info *revs, int argc, const char **argv
 		argv++; argc--;
 	}
 
-	if (revs->max_count == -1 &&
+	/*
+	 * "diff --base" should not combine merges because it was not
+	 * asked to.  "diff -c" should not densify (if the user wants
+	 * dense one, --cc can be explicitly asked for, or just rely
+	 * on the default).
+	 */
+	if (revs->max_count == -1 && !revs->combine_merges &&
 	    (revs->diffopt.output_format & DIFF_FORMAT_PATCH))
 		revs->combine_merges = revs->dense_combined_merges = 1;