diff --git a/src/editfns.c b/src/editfns.c
index 191ea0d9053..10980c96aa1 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -2065,6 +2065,8 @@ a buffer or a string.  But this is deprecated.  */)
 	time_limit = tlim;
     }
 
+  specpdl_ref count = SPECPDL_INDEX ();
+
   /* The rest of the code is not prepared to handle a string SOURCE.  */
   if (!b)
     {
@@ -2077,8 +2079,6 @@ a buffer or a string.  But this is deprecated.  */)
     }
   Lisp_Object source_buffer = make_lisp_ptr (b, Lisp_Vectorlike);
 
-  specpdl_ref count = SPECPDL_INDEX ();
-
   ptrdiff_t diags = size_a + size_b + 3;
   ptrdiff_t bytes_per_diag = 2 * sizeof (ptrdiff_t) + sizeof (int);
   ptrdiff_t surplus_char_bytes = 3 * sizeof (int);