diff --git a/src/PlaceUtils.py b/src/PlaceUtils.py
index 369090cf7..ba6b98e14 100644
--- a/src/PlaceUtils.py
+++ b/src/PlaceUtils.py
@@ -141,6 +141,9 @@ def conv_lat_lon(latitude, longitude, format="D.D4"):
                 if len(l) < 2 or  len(l) > 3:
                     error = True
                 l[0]=l[0].strip()
+                # if no characters to the left of ':', nothing useful is input
+                if len(l[0]) == 0:
+                    return None
                 if l[0][0] == '-':
                     sign = '-'
                     l[0]=l[0][1:]