diff --git a/src/diff.c b/src/diff.c
index c001761..0399e79 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -2266,6 +2266,8 @@
 		p += 9;
 		diff_algorithm_new = XDF_HISTOGRAM_DIFF;
 	    }
+	    else
+		return FAIL;
 	}
 
 	if (*p != ',' && *p != NUL)
diff --git a/src/testdir/gen_opt_test.vim b/src/testdir/gen_opt_test.vim
index a742153..c0e89cf 100644
--- a/src/testdir/gen_opt_test.vim
+++ b/src/testdir/gen_opt_test.vim
@@ -81,7 +81,7 @@
       \ 'cryptmethod': [['', 'zip'], ['xxx']],
       \ 'cscopequickfix': [['', 's-', 's-,c+,e0'], ['xxx', 's,g,d']],
       \ 'debug': [['', 'msg', 'msg', 'beep'], ['xxx']],
-      \ 'diffopt': [['', 'filler', 'icase,iwhite'], ['xxx']],
+      \ 'diffopt': [['', 'filler', 'icase,iwhite'], ['xxx', 'algorithm:xxx', 'algorithm:']],
       \ 'display': [['', 'lastline', 'lastline,uhex'], ['xxx']],
       \ 'eadirection': [['', 'both', 'ver'], ['xxx', 'ver,hor']],
       \ 'encoding': [['latin1'], ['xxx', '']],
diff --git a/src/version.c b/src/version.c
index 3639702..3ed258f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -793,6 +793,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    513,
+/**/
     512,
 /**/
     511,