diff --git a/intern/cycles/SConscript b/intern/cycles/SConscript
index 1a127e364fe..a0e2650ddc6 100644
--- a/intern/cycles/SConscript
+++ b/intern/cycles/SConscript
@@ -49,7 +49,7 @@ if env['OURPLATFORM'] in ('win32-vc', 'win32-mingw', 'linuxcross', 'win64-vc', '
 
 # optimized kernel
 if env['WITH_BF_RAYOPTIMIZATION']:
-    optim_cxxflags = []
+    optim_cxxflags = Split(env['CXXFLAGS'])
 
     if env['OURPLATFORM'] == 'win32-vc':
         optim_cxxflags.append('/arch:SSE2 -D_CRT_SECURE_NO_WARNINGS /fp:fast /EHsc'.split())
diff --git a/intern/cycles/kernel/kernel_light.h b/intern/cycles/kernel/kernel_light.h
index 2791b3abbb6..97ae2d3db87 100644
--- a/intern/cycles/kernel/kernel_light.h
+++ b/intern/cycles/kernel/kernel_light.h
@@ -350,10 +350,9 @@ __device int light_distribution_sample(KernelGlobals *kg, float randt)
 		}
 	}
 
-	first = max(0, first-1);
-	kernel_assert(first >= 0 && first < kernel_data.integrator.num_distribution);
-
-	return first;
+	/* clamping should not be needed but float rounding errors seem to
+	 * make this fail on rare occasions */
+	return clamp(first-1, 0, kernel_data.integrator.num_distribution-1);
 }
 
 /* Generic Light */