diff --git a/src/sky/GSkyRegionRect.cpp b/src/sky/GSkyRegionRect.cpp
index 2123191..0dc1769 100644
--- a/src/sky/GSkyRegionRect.cpp
+++ b/src/sky/GSkyRegionRect.cpp
@@ -753,8 +753,19 @@ bool GSkyRegionRect::overlaps(const GSkyRegion& reg) const
  ***************************************************************************/
 GSkyDir GSkyRegionRect::transform_to_local(const GSkyDir& skydir) const
 {
+    // Get rid of negative right ascension coordinates
+    // (Surely there is a more clever way to to this)
+    double skydir_ra = skydir.ra();
+    if (skydir_ra < 0) {
+        skydir_ra += gammalib::twopi;
+    }
+    double centre_ra = m_centre.ra();
+    if (centre_ra < 0) {
+        centre_ra += gammalib::twopi;
+    }
+
     // Compute separation (in radians)
-    double dx = skydir.ra()  - m_centre.ra();
+    double dx = skydir_ra    - centre_ra;
     double dy = skydir.dec() - m_centre.dec();
 
     // Correction for spherical coordinate system