--- a/src/gt_citation.cpp	2018-08-03 12:16:16.007831564 +0100
+++ b/src/gt_citation.cpp	2018-08-03 12:16:45.224830335 +0100
@@ -387,10 +387,10 @@
         osCitation += primemName;
         bRewriteGeogCitation = TRUE;
 
-        double primemValue = poSRS->GetPrimeMeridian(NULL);
+        double primemValue = poSRS->GetPrimeMeridian();
         if(angUnitName && !EQUAL(angUnitName, "Degree"))
         {
-            double aUnit = poSRS->GetAngularUnits(NULL);
+            double aUnit = poSRS->GetAngularUnits();
             primemValue *= aUnit;
         }
         GTIFKeySet( psGTIF, GeogPrimeMeridianLongGeoKey, TYPE_DOUBLE, 1,