diff --git a/src/channel.c b/src/channel.c
index 581c6f6..0f2e52b 100644
--- a/src/channel.c
+++ b/src/channel.c
@@ -158,6 +158,7 @@
 
 static int did_log_msg = TRUE;
 
+#ifndef PROTO  /* prototype is in vim.h */
     void
 ch_log(channel_T *ch, const char *fmt, ...)
 {
@@ -174,6 +175,14 @@
 	did_log_msg = TRUE;
     }
 }
+#endif
+
+    static void
+ch_error(channel_T *ch, const char *fmt, ...)
+#ifdef __GNUC__
+__attribute__((format(printf, 2, 3)))
+#endif
+    ;
 
     static void
 ch_error(channel_T *ch, const char *fmt, ...)
@@ -1442,8 +1451,8 @@
 	ch_close_part(channel, PART_IN);
     }
     else
-	ch_log(channel, "Still %d more lines to write",
-					  buf->b_ml.ml_line_count - lnum + 1);
+	ch_log(channel, "Still %ld more lines to write",
+				   (long)(buf->b_ml.ml_line_count - lnum + 1));
 }
 
 /*
@@ -1536,8 +1545,8 @@
 	    else if (written > 1)
 		ch_log(channel, "written %d lines to channel", written);
 	    if (lnum < buf->b_ml.ml_line_count)
-		ch_log(channel, "Still %d more lines to write",
-					      buf->b_ml.ml_line_count - lnum);
+		ch_log(channel, "Still %ld more lines to write",
+				       (long)(buf->b_ml.ml_line_count - lnum));
 
 	    in_part->ch_buf_bot = lnum;
 	}
@@ -2081,7 +2090,8 @@
 	{
 	    *rettv = item->jq_value;
 	    if (tv->v_type == VAR_NUMBER)
-		ch_log(channel, "Getting JSON message %d", tv->vval.v_number);
+		ch_log(channel, "Getting JSON message %ld",
+						      (long)tv->vval.v_number);
 	    remove_json_node(head, item);
 	    return OK;
 	}