1 files changed, 14 insertions, 7 deletions
diff --git a/src/nvim/path.c b/src/nvim/path.c
index 3d1def8dd4..7e1183d5db 100644
--- a/src/nvim/path.c
+++ b/src/nvim/path.c
@@ -391,15 +391,22 @@ char *concat_fnames_realloc(char *fname1, const char *fname2, bool sep)
                           fname2, len2, sep);
 }
 
-/*
- * Add a path separator to a file name, unless it already ends in a path
- * separator.
- */
-void add_pathsep(char *p)
+/// Adds a path separator to a filename, unless it already ends in one.
+///
+/// @return `true` if the path separator was added or already existed.
+///         `false` if the filename is too long.
+bool add_pathsep(char *p)
   FUNC_ATTR_NONNULL_ALL
 {
-  if (*p != NUL && !after_pathsep(p, p + strlen(p)))
-    strcat(p, PATHSEPSTR);
+  const size_t len = strlen(p);
+  if (*p != NUL && !after_pathsep(p, p + len)) {
+    const size_t pathsep_len = sizeof(PATHSEPSTR);
+    if (len > MAXPATHL - pathsep_len) {
+      return false;
+    }
+    memcpy(p + len, PATHSEPSTR, pathsep_len);
+  }
+  return true;
 }
 
 /// Get an allocated copy of the full path to a file.