diff --git a/include/mapnik/feature_style_processor_impl.hpp b/include/mapnik/feature_style_processor_impl.hpp
index 4ed3a507a..eade195b3 100644
--- a/include/mapnik/feature_style_processor_impl.hpp
+++ b/include/mapnik/feature_style_processor_impl.hpp
@@ -186,7 +186,7 @@ void feature_style_processor<Processor>::apply(double scale_denom)
             }
         }
     }
-    catch (proj_init_error& ex)
+    catch (proj_init_error const& ex)
     {
         MAPNIK_LOG_ERROR(feature_style_processor) << "feature_style_processor: proj_init_error=" << ex.what();
     }
@@ -228,7 +228,7 @@ void feature_style_processor<Processor>::apply(mapnik::layer const& lyr,
                            names);
         }
     }
-    catch (proj_init_error& ex)
+    catch (proj_init_error const& ex)
     {
         MAPNIK_LOG_ERROR(feature_style_processor) << "feature_style_processor: proj_init_error=" << ex.what();
     }
diff --git a/src/map.cpp b/src/map.cpp
index ca29e3a15..f8fddbd77 100644
--- a/src/map.cpp
+++ b/src/map.cpp
@@ -420,7 +420,7 @@ void Map::zoom_all()
             }
         }
     }
-    catch (proj_init_error & ex)
+    catch (proj_init_error const& ex)
     {
         throw mapnik::config_error(std::string("Projection error during map.zoom_all: ") + ex.what());
     }