diff --git a/ivlpp/lexor.lex b/ivlpp/lexor.lex
index 5641befa5..6917e4dd9 100644
--- a/ivlpp/lexor.lex
+++ b/ivlpp/lexor.lex
@@ -19,7 +19,7 @@
  *    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
 #ifdef HAVE_CVS_IDENT
-#ident "$Id: lexor.lex,v 1.47 2007/05/25 18:21:39 steve Exp $"
+#ident "$Id: lexor.lex,v 1.48 2007/05/30 23:21:20 steve Exp $"
 #endif
 
 # include "config.h"
@@ -118,11 +118,11 @@ static void ifdef_leave(void)
       if (strcmp(istack->path,cur->path) != 0) {
 	    fprintf(stderr, "%s:%u: warning: "
 		    "This `endif matches an ifdef in another file.\n",
-		    istack->path, istack->lineno);
+		    istack->path, istack->lineno+1);
 
 	    fprintf(stderr, "%s:%u:        : "
 		    "This is the odd matched `ifdef.\n",
-		    cur->path, cur->lineno);
+		    cur->path, cur->lineno+1);
       }
 
       free(cur->path);
@@ -316,7 +316,24 @@ W [ \t\b\f]+
       yy_push_state(IFDEF_SUPR);
   }
 
-<IFDEF_TRUE>`else  { BEGIN(IFDEF_FALSE); }
+<IFDEF_TRUE>`elsif{W}[a-zA-Z_][a-zA-Z0-9_$]* {
+      BEGIN(IFDEF_SUPR);
+  }
+<IFDEF_FALSE>`elsif{W}[a-zA-Z_][a-zA-Z0-9_$]* {
+      char*name = strchr(yytext, '`');
+      assert(name);
+      name += 6;
+      name += strspn(name, " \t\b\f");
+
+      if (is_defined(name)) {
+	    BEGIN(IFDEF_TRUE);
+      } else {
+	    BEGIN(IFDEF_FALSE);
+      }
+  }
+<IFDEF_SUPR>`elsif{W}[a-zA-Z_][a-zA-Z0-9_$]* {  }
+
+<IFDEF_TRUE>`else  { BEGIN(IFDEF_SUPR); }
 <IFDEF_FALSE>`else { BEGIN(IFDEF_TRUE); }
 <IFDEF_SUPR>`else  {  }
 
@@ -329,6 +346,42 @@ W [ \t\b\f]+
 
 <IFDEF_FALSE,IFDEF_TRUE,IFDEF_SUPR>`endif { ifdef_leave(); yy_pop_state(); }
 
+`ifdef {
+      fprintf(stderr, "%s:%u: `ifdef without a macro name - ignored.\n",
+              istack->path, istack->lineno+1);
+      error_count += 1;
+  }
+
+`ifndef {
+      fprintf(stderr, "%s:%u: `ifndef without a macro name - ignored.\n",
+              istack->path, istack->lineno+1);
+      error_count += 1;
+  }
+
+`elsif {
+      fprintf(stderr, "%s:%u: `elsif without a macro name - ignored.\n",
+              istack->path, istack->lineno+1);
+      error_count += 1;
+  }
+
+`elsif{W}[a-zA-Z_][a-zA-Z0-9_$]* {
+      fprintf(stderr, "%s:%u: `elsif without a matching `ifdef - ignored.\n",
+              istack->path, istack->lineno+1);
+      error_count += 1;
+  }
+
+`else {
+      fprintf(stderr, "%s:%u: `else without a matching `ifdef - ignored.\n",
+              istack->path, istack->lineno+1);
+      error_count += 1;
+  }
+
+`endif {
+      fprintf(stderr, "%s:%u: `endif without a matching `ifdef - ignored.\n",
+              istack->path, istack->lineno+1);
+      error_count += 1;
+  }
+
   /* This pattern notices macros and arranges for them to be replaced. */
 `[a-zA-Z][a-zA-Z0-9_$]* { def_match(); }
 
@@ -766,7 +819,7 @@ static void lexor_done()
 	    ifdef_stack = cur->next;
 
 	    fprintf(stderr, "%s:%u: error: This `ifdef lacks an `endif.\n",
-		    cur->path, cur->lineno);
+		    cur->path, cur->lineno+1);
 
 	    free(cur->path);
 	    free(cur);