1 files changed, 12 insertions, 2 deletions

diff --git a/editors/patch.c b/editors/patch.c
index 13785ef46..cb25e4140 100644
--- a/editors/patch.c
+++ b/editors/patch.c
@@ -345,6 +345,8 @@ done:
 // state 1: Found +++ file indicator, look for @@
 // state 2: In hunk: counting initial context lines
 // state 3: In hunk: getting body
+// Like GNU patch, we don't require a --- line before the +++, and
+// also allow the --- after the +++ line.
 
 int patch_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int patch_main(int argc UNUSED_PARAM, char **argv)
@@ -412,7 +414,7 @@ int patch_main(int argc UNUSED_PARAM, char **argv)
                 }
 
                 // Open a new file?
-                if (!strncmp("--- ", patchline, 4) || !strncmp("+++ ", patchline, 4)) {
+                if (is_prefixed_with(patchline, "--- ") || is_prefixed_with(patchline, "+++ ")) {
                         char *s, **name = reverse ? &newname : &oldname;
                         int i;
 
@@ -444,7 +446,7 @@ int patch_main(int argc UNUSED_PARAM, char **argv)
 
                 // Start a new hunk?  Usually @@ -oldline,oldlen +newline,newlen @@
                 // but a missing ,value means the value is 1.
-                } else if (state == 1 && !strncmp("@@ -", patchline, 4)) {
+                } else if (state == 1 && is_prefixed_with(patchline, "@@ -")) {
                         int i;
                         char *s = patchline+4;
 
@@ -462,6 +464,14 @@ int patch_main(int argc UNUSED_PARAM, char **argv)
                         TT.context = 0;
                         state = 2;
 
+                        // If the --- line is missing or malformed, either oldname
+                        // or (for -R) newname could be NULL -- but not both.  Like
+                        // GNU patch, proceed based on the +++ line, and avoid SEGVs.
+                        if (!oldname)
+                                oldname = xstrdup("MISSING_FILENAME");
+                        if (!newname)
+                                newname = xstrdup("MISSING_FILENAME");
+
                         // If this is the first hunk, open the file.
                         if (TT.filein == -1) {
                                 int oldsum, newsum, empty = 0;