diff --git a/changes/bug21496 b/changes/bug21496
new file mode 100644
index 0000000000..24ac85a769
--- /dev/null
+++ b/changes/bug21496
@@ -0,0 +1,4 @@
+  o Minor features (safety):
+    - Add an explict check to extrainfo_parse_entry_from_string() for NULL
+      inputs. We don't believe this can actually happen, but it may help
+      silence a warning from the Clang analyzer. Closes ticket 21496.
diff --git a/src/or/routerparse.c b/src/or/routerparse.c
index 0336c035b4..c4f329513c 100644
--- a/src/or/routerparse.c
+++ b/src/or/routerparse.c
@@ -2030,6 +2030,9 @@ extrainfo_parse_entry_from_string(const char *s, const char *end,
    * parse that's covered by the hash. */
   int can_dl_again = 0;
 
+  if (BUG(s == NULL))
+    return NULL;
+
   if (!end) {
     end = s + strlen(s);
   }