diff --git a/src/Makefile b/src/Makefile
index 52c74f2..b5d39ec 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -2177,6 +2177,7 @@
 	test_pyx2 \
 	test_pyx3 \
 	test_quickfix \
+	test_recover \
 	test_regexp_latin \
 	test_regexp_utf8 \
 	test_reltime \
diff --git a/src/memline.c b/src/memline.c
index 5874b5d..df799b1 100644
--- a/src/memline.c
+++ b/src/memline.c
@@ -1863,8 +1863,10 @@
 	    else
 	    {
 #if defined(UNIX) || defined(WIN3264)
-		p = dir_name + STRLEN(dir_name);
-		if (after_pathsep(dir_name, p) && p[-1] == p[-2])
+		int	len = STRLEN(dir_name);
+
+		p = dir_name + len;
+		if (after_pathsep(dir_name, p) && len > 1 && p[-1] == p[-2])
 		{
 		    /* Ends with '//', Use Full path for swap name */
 		    tail = make_percent_swname(dir_name, fname_res);
@@ -3922,8 +3924,10 @@
 #endif
 
 #if defined(UNIX) || defined(WIN3264)  /* Need _very_ long file names */
-    s = dir_name + STRLEN(dir_name);
-    if (after_pathsep(dir_name, s) && s[-1] == s[-2])
+    int		len = STRLEN(dir_name);
+
+    s = dir_name + len;
+    if (after_pathsep(dir_name, s) && len > 1 && s[-1] == s[-2])
     {			       /* Ends with '//', Use Full path */
 	r = NULL;
 	if ((s = make_percent_swname(dir_name, fname)) != NULL)
diff --git a/src/testdir/test_alot.vim b/src/testdir/test_alot.vim
index d43ae4f..ef0edc7 100644
--- a/src/testdir/test_alot.vim
+++ b/src/testdir/test_alot.vim
@@ -34,6 +34,7 @@
 source test_partial.vim
 source test_popup.vim
 source test_put.vim
+source test_recover.vim
 source test_reltime.vim
 source test_searchpos.vim
 source test_set.vim
diff --git a/src/testdir/test_recover.vim b/src/testdir/test_recover.vim
new file mode 100644
index 0000000..aa291b1
--- /dev/null
+++ b/src/testdir/test_recover.vim
@@ -0,0 +1,14 @@
+" Test :recover
+
+func Test_recover_root_dir()
+  " This used to access invalid memory.
+  split Xtest
+  set dir=/
+  call assert_fails('recover', 'E305:')
+  close!
+
+  call assert_fails('split Xtest', 'E303:')
+  set dir&
+endfunc
+
+" TODO: move recover tests from test78.in to here.
diff --git a/src/version.c b/src/version.c
index df77e82..73f9929 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    337,
+/**/
     336,
 /**/
     335,