diff --git a/src/minibuf.c b/src/minibuf.c
index 58adde1bf66..a1cbf4747f5 100644
--- a/src/minibuf.c
+++ b/src/minibuf.c
@@ -1502,34 +1502,30 @@ DEFUN ("read-buffer", Fread_buffer, Sread_buffer, 1, 4, 0,
   specbind (Qcompletion_ignore_case,
 	    read_buffer_completion_ignore_case ? Qt : Qnil);

-  if (NILP (Vread_buffer_function))
-    {
-      if (!NILP (def))
-	{
-	  /* A default value was provided: we must change PROMPT,
-	     editing the default value in before the colon.  To achieve
-	     this, we replace PROMPT with a substring that doesn't
-	     contain the terminal space and colon (if present).  They
-	     are then added back using Fformat.  */
+  /* For backward compatibility we accept prompt strings ending with a
+     colon and a space, but we have to delete them, if present, before
+     passing PROMPT to `format-prompt', which automatically appends
+     these characters to PROMPT.  */

-	  if (STRINGP (prompt))
-	    {
-	      s = SSDATA (prompt);
-	      len = SBYTES (prompt);
-	      if (len >= 2 && s[len - 2] == ':' && s[len - 1] == ' ')
-		len = len - 2;
-	      else if (len >= 1 && (s[len - 1] == ':' || s[len - 1] == ' '))
-		len--;
-
-	      prompt = make_specified_string (s, -1, len,
-					      STRING_MULTIBYTE (prompt));
-	    }
+  if (STRINGP (prompt))
+    {
+      s = SSDATA (prompt);
+      len = SBYTES (prompt);
+      if (len >= 2 && s[len - 2] == ':' && s[len - 1] == ' ')
+	len = len - 2;
+      else if (len >= 1 && (s[len - 1] == ':' || s[len - 1] == ' '))
+	len--;
+
+      prompt = make_specified_string (s, -1, len,
+				      STRING_MULTIBYTE (prompt));
+    }

-	  prompt = CALLN (Ffuncall, intern("format-prompt"),
-			  prompt,
-			  CONSP (def) ? XCAR (def) : def);
-	}
+  prompt = CALLN (Ffuncall, intern("format-prompt"),
+		  prompt,
+		  CONSP (def) ? XCAR (def) : def);

+  if (NILP (Vread_buffer_function))
+    {
       result = Fcompleting_read (prompt, intern ("internal-complete-buffer"),
 				 predicate, require_match, Qnil,
 				 Qbuffer_name_history, def, Qnil);