diff -p -up rpm-4.4.2.3/build/parseSpec.c.pix rpm-4.4.2.3/build/parseSpec.c
--- rpm-4.4.2.3/build/parseSpec.c.pix	2008-05-27 11:12:45.000000000 +0200
+++ rpm-4.4.2.3/build/parseSpec.c	2008-05-28 13:26:08.000000000 +0200
@@ -136,6 +136,24 @@ static void forceIncludeFile(Spec spec, 
     spec->fileStack = ofi;
 }
 
+static int begins_with(const char *s, const char *prefix)
+{
+  return strncmp(s, prefix, strlen(prefix)) == 0;
+}
+
+static int isCommentedDefine(const char *line)
+{
+    const char *p = line;
+
+    SKIPSPACE(p);
+    if (*p++ == '#') {
+        SKIPSPACE(p);
+	if (begins_with(p, "%define") &&
+	    xisspace(p[strlen("%define")])) return 1;
+    }
+    return 0;
+}
+
 /**
  */
 /*@-boundswrite@*/
@@ -158,6 +176,11 @@ static int copyNextLineFromOFI(Spec spec
 	*to++ = '\0';
 	ofi->readPtr = from;
 
+	if (isCommentedDefine(spec->lbuf)) {
+	    rpmError(RPMERR_BADSPEC, _("%s:%d: #%%define is forbidden, use #define to comment a %%define\n"), ofi->fileName, ofi->lineNum);
+	    return RPMERR_BADSPEC;
+	}
+
 	/* Check if we need another line before expanding the buffer. */
 	for (p = spec->lbuf; *p; p++) {
 	    switch (*p) {