diff --git a/lexor.lex b/lexor.lex
index b70936c73..ad0df6906 100644
--- a/lexor.lex
+++ b/lexor.lex
@@ -517,6 +517,12 @@ S [afpnumkKMGT]
 	   << endl;
   }
 
+^{W}?`elsif{W}?.* {
+      cerr << yylloc.text << ":" << yylloc.first_line <<
+	    ": warning: `elsif not supported. Use an external preprocessor."
+	   << endl;
+  }
+
 ^{W}?`endif{W}?.* {
       cerr << yylloc.text << ":" << yylloc.first_line <<
 	    ": warning: `endif not supported. Use an external preprocessor."
@@ -529,6 +535,12 @@ S [afpnumkKMGT]
 	   << endl;
   }
 
+^{W}?`ifndef{W}?.* {
+      cerr << yylloc.text << ":" << yylloc.first_line <<
+	    ": warning: `ifndef not supported. Use an external preprocessor."
+	   << endl;
+  }
+
 ^`include{W}?.* {
       cerr << yylloc.text << ":" << yylloc.first_line <<
 	    ": warning: `include not supported. Use an external preprocessor."