diff --git a/intern/cycles/blender/addon/version_update.py b/intern/cycles/blender/addon/version_update.py
index 2208849752c..07da3202b53 100644
--- a/intern/cycles/blender/addon/version_update.py
+++ b/intern/cycles/blender/addon/version_update.py
@@ -243,11 +243,15 @@ def do_versions(self):
                         layer.samples *= layer.samples
                     cscene["use_square_samples"] = False
 
-            # Disable light tree for existing scenes.
             if version <= (3, 5, 3):
                 cscene = scene.cycles
+                # Disable light tree for existing scenes.
                 if not cscene.is_property_set("use_light_tree"):
                     cscene.use_light_tree = False
+                # Sampling pattern settings are hidden behind a debug menu. Switch to the
+                # default faster and fully featured (Supports Scrambling Distance)
+                # Tabulated Sobol.
+                cscene.sampling_pattern = 'TABULATED_SOBOL'
 
         # Lamps
         for light in bpy.data.lights:
diff --git a/intern/cycles/kernel/osl/closures_setup.h b/intern/cycles/kernel/osl/closures_setup.h
index 48b2367c6d1..514134447f4 100644
--- a/intern/cycles/kernel/osl/closures_setup.h
+++ b/intern/cycles/kernel/osl/closures_setup.h
@@ -831,7 +831,7 @@ ccl_device void osl_closure_bssrdf_setup(KernelGlobals kg,
   /* create one closure per color channel */
   bssrdf->albedo = closure->albedo;
   bssrdf->N = maybe_ensure_valid_specular_reflection(sd, closure->N);
-  bssrdf->alpha = sqr(closure->roughness);
+  bssrdf->alpha = closure->roughness;
   bssrdf->ior = closure->ior;
   bssrdf->anisotropy = closure->anisotropy;
 
diff --git a/intern/cycles/kernel/osl/shaders/node_principled_bsdf.osl b/intern/cycles/kernel/osl/shaders/node_principled_bsdf.osl
index 2b0e1d1686e..816592513bd 100644
--- a/intern/cycles/kernel/osl/shaders/node_principled_bsdf.osl
+++ b/intern/cycles/kernel/osl/shaders/node_principled_bsdf.osl
@@ -74,7 +74,7 @@ shader node_principled_bsdf(string distribution = "multi_ggx",
                                          SubsurfaceScale * SubsurfaceRadius,
                                          BaseColor,
                                          "roughness",
-                                         Roughness,
+                                         r2,
                                          "ior",
                                          subsurface_ior,
                                          "anisotropy",
@@ -82,14 +82,16 @@ shader node_principled_bsdf(string distribution = "multi_ggx",
       BSDF = mix(BSDF, BaseColor * SubsurfBSDF, subsurface_weight);
     }
 
-    /* Apply specular tint */
-    color F0 = f0 * specular_tint;
-    color F90 = color(1.0);
+    if (eta != 1.0) {
+      /* Apply specular tint */
+      color F0 = f0 * specular_tint;
+      color F90 = color(1.0);
 
-    BSDF = layer(
-        generalized_schlick_bsdf(
-            Normal, T, color(1.0), color(0.0), alpha_x, alpha_y, F0, F90, -eta, distribution),
-        BSDF);
+      BSDF = layer(
+          generalized_schlick_bsdf(
+              Normal, T, color(1.0), color(0.0), alpha_x, alpha_y, F0, F90, -eta, distribution),
+          BSDF);
+    }
   }
 
   closure color TransmissionBSDF = 0;
diff --git a/intern/cycles/kernel/svm/closure.h b/intern/cycles/kernel/svm/closure.h
index c2bd9f09499..d7cd0dd8c6f 100644
--- a/intern/cycles/kernel/svm/closure.h
+++ b/intern/cycles/kernel/svm/closure.h
@@ -327,8 +327,19 @@ ccl_device
         }
       }
 
+      /* Apply IOR adjustment */
+      float eta = ior;
+      float f0 = F0_from_ior(eta);
+      if (specular_ior_level != 0.5f) {
+        f0 *= 2.0f * specular_ior_level;
+        eta = ior_from_F0(f0);
+        if (ior < 1.0f) {
+          eta = 1.0f / eta;
+        }
+      }
+
       /* Specular component */
-      if (reflective_caustics) {
+      if (reflective_caustics && eta != 1.0f) {
         ccl_private MicrofacetBsdf *bsdf = (ccl_private MicrofacetBsdf *)bsdf_alloc(
             sd, sizeof(MicrofacetBsdf), weight);
         ccl_private FresnelGeneralizedSchlick *fresnel =
@@ -337,17 +348,6 @@ ccl_device
                              NULL;
 
         if (bsdf && fresnel) {
-          /* Apply IOR adjustment */
-          float eta = ior;
-          float f0 = F0_from_ior(eta);
-          if (specular_ior_level != 0.5f) {
-            f0 *= 2.0f * specular_ior_level;
-            eta = ior_from_F0(f0);
-            if (ior < 1.0f) {
-              eta = 1.0f / eta;
-            }
-          }
-
           bsdf->N = valid_reflection_N;
           bsdf->ior = eta;
           bsdf->T = T;
@@ -383,7 +383,7 @@ ccl_device
         bssrdf->albedo = rgb_to_spectrum(base_color);
         bssrdf->N = maybe_ensure_valid_specular_reflection(sd, N);
         bssrdf->alpha = sqr(roughness);
-        bssrdf->ior = ior;
+        bssrdf->ior = eta;
         bssrdf->anisotropy = stack_load_float(stack, data_subsurf.w);
         if (subsurface_method == CLOSURE_BSSRDF_RANDOM_WALK_SKIN_ID) {
           bssrdf->ior = stack_load_float(stack, data_subsurf.x);