diff --git a/libowlps/libowlps.c b/libowlps/libowlps.c
index 1e44c1a..d9a2927 100644
--- a/libowlps/libowlps.c
+++ b/libowlps/libowlps.c
@@ -181,8 +181,8 @@ owl_timestamp owl_time_elapsed(const owl_timestamp d1,
   elapsed.tv_sec = abs(d1.tv_sec - d2.tv_sec) ;
   elapsed.tv_nsec = abs(d1.tv_nsec - d2.tv_nsec) ;
 #ifdef DEBUG
-  printf("time_elapsed(): %"PRIu64"ms\n",
-         owl_timestamp_to_ms(elapsed)) ;
+  fprintf(stderr, "time_elapsed(): %"PRIu64"ms\n",
+          owl_timestamp_to_ms(elapsed)) ;
 #endif
   return elapsed ;
 }
@@ -425,7 +425,7 @@ void owl_sigint_handler(int num)
   run = FALSE ;
 
 #ifdef DEBUG
-  printf("\nSignal received: end.\n");
+  fprintf(stderr, "\nSignal received: end.\n");
 #endif // DEBUG
   fflush(NULL) ;
 }