diff --git a/simgear/scene/viewer/Compositor.cxx b/simgear/scene/viewer/Compositor.cxx
index c229b49a..c4bdc88f 100644
--- a/simgear/scene/viewer/Compositor.cxx
+++ b/simgear/scene/viewer/Compositor.cxx
@@ -177,7 +177,8 @@ Compositor::update(const osg::Matrix &view_matrix,
     SGGeod camera_pos_geod = SGGeod::fromCart(
         SGVec3d(camera_pos.x(), camera_pos.y(), camera_pos.z()));
 
-    double left, right, bottom, top, zNear, zFar;
+    double left = 0.0, right = 0.0, bottom = 0.0, top = 0.0,
+        zNear = 0.0, zFar = 0.0;
     proj_matrix.getFrustum(left, right, bottom, top, zNear, zFar);
 
     osg::Matrixf prev_view_matrix, prev_view_matrix_inv;
diff --git a/simgear/scene/viewer/CompositorPass.cxx b/simgear/scene/viewer/CompositorPass.cxx
index d1d23303..9cdb2c35 100644
--- a/simgear/scene/viewer/CompositorPass.cxx
+++ b/simgear/scene/viewer/CompositorPass.cxx
@@ -502,7 +502,8 @@ public:
 
         // Calculate the light's point of view transformation matrices.
         // Taken from Project Rembrandt.
-        double left, right, bottom, top, zNear, zFar;
+        double left = 0.0, right = 0.0, bottom = 0.0, top = 0.0,
+            zNear = 0.0, zFar = 0.0;
         proj_matrix.getFrustum(left, right, bottom, top, zNear, zFar);
 
         osg::BoundingSphere bs;