diff --git a/src/calculations/calculations_transformations.c b/src/calculations/calculations_transformations.c
index 770fdea..fad9882 100644
--- a/src/calculations/calculations_transformations.c
+++ b/src/calculations/calculations_transformations.c
@@ -194,6 +194,11 @@ double
   y = cos (declination) * sin (time_sidereal - right_ascension);
 
   azimuth = atan2 (-y, -x);
+  /*
+   * Exclude negative results
+   */
+  if (azimuth < 0)
+    azimuth += 2*M_PI;
 
   elevation = asin (sin (latitude) * sin (declination)
                     + cos (latitude) * cos (declination) * cos (time_sidereal - right_ascension));