diff --git a/admin/halog/halog.c b/admin/halog/halog.c
index 884a606e8..3d8941140 100644
--- a/admin/halog/halog.c
+++ b/admin/halog/halog.c
@@ -123,6 +123,22 @@ struct url_stat {
 #define FILT2_PRESERVE_QUERY    0x02
 #define FILT2_EXTRACT_CAPTURE   0x04
 
+#define FILT_OUTPUT_FMT   (FILT_COUNT_ONLY| \
+			   FILT_COUNT_STATUS| \
+			   FILT_COUNT_SRV_STATUS| \
+			   FILT_COUNT_COOK_CODES| \
+			   FILT_COUNT_TERM_CODES| \
+			   FILT_COUNT_URL_ONLY| \
+			   FILT_COUNT_URL_COUNT| \
+			   FILT_COUNT_URL_ERR| \
+			   FILT_COUNT_URL_TAVG| \
+			   FILT_COUNT_URL_TTOT| \
+			   FILT_COUNT_URL_TAVGO| \
+			   FILT_COUNT_URL_TTOTO| \
+			   FILT_COUNT_URL_BAVG| \
+			   FILT_COUNT_URL_BTOT| \
+			   FILT_COUNT_IP_COUNT)
+
 unsigned int filter = 0;
 unsigned int filter2 = 0;
 unsigned int filter_invert = 0;
@@ -192,7 +208,7 @@ void help()
 	       "                         you can also use -n to start from earlier then field %d\n"
 	       " -query                  preserve the query string for per-URL (-u*) statistics\n"
 	       "\n"
-	       "Output format - only one may be used at a time\n"
+	       "Output format - **only one** may be used at a time\n"
 	       " -c    only report the number of lines that would have been printed\n"
 	       " -pct  output connect and response times percentiles\n"
 	       " -st   output number of requests per HTTP status code\n"
@@ -898,6 +914,9 @@ int main(int argc, char **argv)
 	if (!filter && !filter2)
 		die("No action specified.\n");
 
+	if ((filter & FILT_OUTPUT_FMT) & ((filter & FILT_OUTPUT_FMT) - 1))
+		die("Please, set only one output filter.\n");
+
 	if (filter & FILT_ACC_COUNT && !filter_acc_count)
 		filter_acc_count=1;