diff --git a/src/microhttpd/connection.c b/src/microhttpd/connection.c
index 50a5de32..35dd96ab 100644
--- a/src/microhttpd/connection.c
+++ b/src/microhttpd/connection.c
@@ -4273,7 +4273,8 @@ get_request_line_inner (struct MHD_Connection *c)
       if (is_empty_line)
       {
         if ((! skip_unlimited_empty_lines) &&
-            (((skip_several_empty_lines) ? MHD_MAX_EMPTY_LINES_SKIP : 1) <
+            (((unsigned int) ((skip_several_empty_lines) ?
+                              MHD_MAX_EMPTY_LINES_SKIP : 1)) <
              c->rq.hdrs.rq_line.skipped_empty_lines))
         {
           connection_close_error (c,
@@ -4823,7 +4824,7 @@ send_redirect_fixed_rq_target (struct MHD_Connection *c)
 static bool
 process_request_target (struct MHD_Connection *c)
 {
-#if _DEBUG
+#ifdef _DEBUG
   size_t params_len;
 #endif /* _DEBUG */
   mhd_assert (MHD_CONNECTION_REQ_LINE_RECEIVING == c->state);
@@ -4849,7 +4850,7 @@ process_request_target (struct MHD_Connection *c)
 
   if (NULL != c->rq.hdrs.rq_line.rq_tgt_qmark)
   {
-#if _DEBUG
+#ifdef _DEBUG
     params_len =
       c->rq.hdrs.rq_line.rq_tgt_len
       - (size_t) (c->rq.hdrs.rq_line.rq_tgt_qmark - c->rq.hdrs.rq_line.rq_tgt);
@@ -4865,7 +4866,7 @@ process_request_target (struct MHD_Connection *c)
       return false;
     }
   }
-#if _DEBUG
+#ifdef _DEBUG
   else
     params_len = 0;
 #endif /* _DEBUG */
diff --git a/src/microhttpd/digestauth.c b/src/microhttpd/digestauth.c
index ed2610c2..85a46260 100644
--- a/src/microhttpd/digestauth.c
+++ b/src/microhttpd/digestauth.c
@@ -333,7 +333,7 @@ struct DigestAlgorithm
   /**
    * Buffer for hex-print of the final digest.
    */
-#if _DEBUG
+#ifdef _DEBUG
   bool uninitialised; /**< The structure has been not set-up */
   bool algo_selected; /**< The algorithm has been selected */
   bool ready_for_hashing; /**< The structure is ready to hash data */
diff --git a/src/microhttpd/response.c b/src/microhttpd/response.c
index 3f278689..c594d4f7 100644
--- a/src/microhttpd/response.c
+++ b/src/microhttpd/response.c
@@ -1933,7 +1933,9 @@ enum MHD_Result
 MHD_response_execute_upgrade_ (struct MHD_Response *response,
                                struct MHD_Connection *connection)
 {
+#ifdef HTTPS_SUPPORT
   struct MHD_Daemon *daemon = connection->daemon;
+#endif /* HTTPS_SUPPORT */
   struct MHD_UpgradeResponseHandle *urh;
   size_t rbo;
 
diff --git a/src/tools/perf_replies.c b/src/tools/perf_replies.c
index fdec7e8e..38ee701d 100644
--- a/src/tools/perf_replies.c
+++ b/src/tools/perf_replies.c
@@ -1744,8 +1744,7 @@ get_mhd_response_size (void)
     return "8 KB (medium)";
   else if (tool_params.large)
     return "1 MB (large)";
-  abort ();
-  return "";
+  return "!!internal error!!";
 }