diff --git a/openair1/PHY/TOOLS/nr_phy_scope.c b/openair1/PHY/TOOLS/nr_phy_scope.c
index 176404f26c..1d6a279c91 100644
--- a/openair1/PHY/TOOLS/nr_phy_scope.c
+++ b/openair1/PHY/TOOLS/nr_phy_scope.c
@@ -243,7 +243,7 @@ static void genericWaterFall (OAIgraph_t *graph, scopeSample_t *values, const in
   for (int pix=0; pix<graph->w; pix++) {
     scopeSample_t *end=values+(pix+1)*samplesPerPixel;
     end-=2;
-    AssertFatal(end <= values+datasize,"diff : %lu", end-values+datasize);
+    AssertFatal(end <= values+datasize,"diff : %u", end-values+datasize);
     double val=0;
 
     for (scopeSample_t *s=values+(pix)*samplesPerPixel;