diff --git a/indra/llrender/llshadermgr.cpp b/indra/llrender/llshadermgr.cpp
index 4807c122263..0c3fbcace8e 100644
--- a/indra/llrender/llshadermgr.cpp
+++ b/indra/llrender/llshadermgr.cpp
@@ -1313,6 +1313,7 @@ void LLShaderMgr::initAttribsAndUniforms()
 
     mReservedUniforms.push_back("minimum_alpha");
     mReservedUniforms.push_back("emissive_brightness");
+    mReservedUniforms.push_back("alpha_gamma");
 
     // Deferred
     mReservedUniforms.push_back("shadow_matrix");
diff --git a/indra/llrender/llshadermgr.h b/indra/llrender/llshadermgr.h
index 46788841a5d..2fd76a34ffe 100644
--- a/indra/llrender/llshadermgr.h
+++ b/indra/llrender/llshadermgr.h
@@ -156,6 +156,7 @@ class LLShaderMgr
 
         MINIMUM_ALPHA,                      //  "minimum_alpha"
         EMISSIVE_BRIGHTNESS,                //  "emissive_brightness"
+        ALPHA_GAMMA,                        //  "alpha_gamma"
 
         DEFERRED_SHADOW_MATRIX,             //  "shadow_matrix"
         DEFERRED_ENV_MAT,                   //  "env_mat"
diff --git a/indra/newview/app_settings/settings.xml b/indra/newview/app_settings/settings.xml
index d64f82d3036..b59546f3fa1 100644
--- a/indra/newview/app_settings/settings.xml
+++ b/indra/newview/app_settings/settings.xml
@@ -7478,6 +7478,17 @@
     <key>Value</key>
     <integer>0</integer>
   </map>
+  <key>RenderLegacyAlphaGamma</key>
+  <map>
+    <key>Comment</key>
+    <string>Gamma correction factor (clamped between 1.0 and 2.2) used to render non-PBR faces with alpha blend. 1.0 to disable.</string>
+    <key>Persist</key>
+    <integer>1</integer>
+    <key>Type</key>
+    <string>F32</string>
+    <key>Value</key>
+    <real>1.8</real>
+  </map>
   <key>RenderLocalLightCount</key>
   <map>
     <key>Comment</key>
diff --git a/indra/newview/app_settings/shaders/class2/deferred/alphaF.glsl b/indra/newview/app_settings/shaders/class2/deferred/alphaF.glsl
index cc9d72fae61..7d458f8c936 100644
--- a/indra/newview/app_settings/shaders/class2/deferred/alphaF.glsl
+++ b/indra/newview/app_settings/shaders/class2/deferred/alphaF.glsl
@@ -37,6 +37,7 @@ uniform mat3 env_mat;
 uniform vec3 sun_dir;
 uniform vec3 moon_dir;
 uniform int classic_mode;
+uniform float alpha_gamma;
 
 #ifdef USE_DIFFUSE_TEX
 uniform sampler2D diffuseMap;
@@ -215,7 +216,7 @@ void main()
     }
 
     color.rgb = diffuse_srgb.rgb;
-    color.a = final_alpha;
+    color.a = pow(final_alpha, alpha_gamma);
 
 #else // FOR_IMPOSTOR
 
@@ -263,7 +264,7 @@ void main()
 
     vec4 color = vec4(0.0);
 
-    color.a   = final_alpha;
+    color.a = pow(final_alpha, alpha_gamma);
 
     color.rgb = irradiance;
     if (classic_mode > 0)
diff --git a/indra/newview/app_settings/shaders/class3/deferred/materialF.glsl b/indra/newview/app_settings/shaders/class3/deferred/materialF.glsl
index 5708fc319fa..6327299d1b0 100644
--- a/indra/newview/app_settings/shaders/class3/deferred/materialF.glsl
+++ b/indra/newview/app_settings/shaders/class3/deferred/materialF.glsl
@@ -37,6 +37,7 @@
 uniform float emissive_brightness;  // fullbright flag, 1.0 == fullbright, 0.0 otherwise
 uniform int sun_up_factor;
 uniform int classic_mode;
+uniform float alpha_gamma;
 
 vec4 applySkyAndWaterFog(vec3 pos, vec3 additive, vec3 atten, vec4 color);
 vec3 scaleSoftClipFragLinear(vec3 l);
@@ -420,7 +421,7 @@ void main()
 
     glare *= 1.0-emissive;
     glare = min(glare, 1.0);
-    float al = max(diffcol.a, glare) * vertex_color.a;
+    float al = pow(max(diffcol.a, glare) * vertex_color.a, alpha_gamma);
     float final_scale = 1;
     if (classic_mode > 0)
         final_scale = 1.1;
diff --git a/indra/newview/lldrawpoolalpha.cpp b/indra/newview/lldrawpoolalpha.cpp
index 87b6ce6cb3a..c51e1c6c3a7 100644
--- a/indra/newview/lldrawpoolalpha.cpp
+++ b/indra/newview/lldrawpoolalpha.cpp
@@ -595,6 +595,11 @@ void LLDrawPoolAlpha::renderAlpha(U32 mask, bool depth_only, bool rigged)
         above_water = !above_water;
     }
 
+     // Gamma correction factor for alpha faces without PBR material, in PBR
+    // rendering mode. HB
+    static LLCachedControl<F32> legacy_gamma(gSavedSettings,
+                                             "RenderLegacyAlphaGamma");
+    F32 alpha_gamma = llclamp((F32)legacy_gamma, 1.f, 2.2f);
 
     for (LLCullResult::sg_iterator i = begin; i != end; ++i)
     {
@@ -760,6 +765,8 @@ void LLDrawPoolAlpha::renderAlpha(U32 mask, bool depth_only, bool rigged)
                         current_shader->uniform4f(LLShaderMgr::SPECULAR_COLOR, spec_color.mV[VRED], spec_color.mV[VGREEN], spec_color.mV[VBLUE], spec_color.mV[VALPHA]);
                         current_shader->uniform1f(LLShaderMgr::ENVIRONMENT_INTENSITY, env_intensity);
                         current_shader->uniform1f(LLShaderMgr::EMISSIVE_BRIGHTNESS, brightness);
+                        // Fix for alpha gamma on non-PBR (legacy) faces. HB
+                        current_shader->uniform1f(LLShaderMgr::ALPHA_GAMMA, params.mHasPBR ? 1.f : alpha_gamma);
                     }
                 }
 
diff --git a/indra/newview/llspatialpartition.h b/indra/newview/llspatialpartition.h
index 3aaa3d60e87..587d5367a74 100644
--- a/indra/newview/llspatialpartition.h
+++ b/indra/newview/llspatialpartition.h
@@ -136,6 +136,8 @@ class LLDrawInfo final : public LLRefCount
     U8   mShiny = 0;
     bool mFullbright = false;
     bool mHasGlow = false;
+	// Set to 'true' when a PBR material is actually used to render this face. HB
+    bool mHasPBR = false;
 
     struct CompareTexture
     {
diff --git a/indra/newview/llvovolume.cpp b/indra/newview/llvovolume.cpp
index 80fc486a103..202b42b7278 100644
--- a/indra/newview/llvovolume.cpp
+++ b/indra/newview/llvovolume.cpp
@@ -5372,10 +5372,9 @@ void LLVolumeGeometryManager::registerFace(LLSpatialGroup* group, LLFace* facep,
 
     U8 index = facep->getTextureIndex();
 
+    bool has_pbr = false;
     LLMaterial* mat = nullptr;
-
     LLUUID mat_id;
-
     auto* gltf_mat = (LLFetchedGLTFMaterial*)te->getGLTFRenderMaterial();
     llassert(gltf_mat == nullptr || dynamic_cast<LLFetchedGLTFMaterial*>(te->getGLTFRenderMaterial()) != nullptr);
     if (gltf_mat != nullptr)
@@ -5384,6 +5383,7 @@ void LLVolumeGeometryManager::registerFace(LLSpatialGroup* group, LLFace* facep,
         if (!facep->hasMedia() || (tex && tex->getType() != LLViewerTexture::MEDIA_TEXTURE))
         { // no media texture, face texture will be unused
             tex = nullptr;
+            has_pbr = true;
         }
     }
     else
@@ -5447,6 +5447,7 @@ void LLVolumeGeometryManager::registerFace(LLSpatialGroup* group, LLFace* facep,
         info->mCount + facep->getIndicesCount() <= (U32) gGLManager.mGLMaxIndexRange &&
 #endif
         info->mMaterialID == mat_id &&
+        info->mHasPBR == has_pbr &&
         info->mFullbright == fullbright &&
         info->mBump == bump &&
         (!mat || (info->mShiny == shiny)) && // need to break batches when a material is shared, but legacy settings are different
@@ -5501,6 +5502,7 @@ void LLVolumeGeometryManager::registerFace(LLSpatialGroup* group, LLFace* facep,
         draw_info->mShaderMask = shader_mask;
         draw_info->mAvatar = facep->mAvatar;
         draw_info->mSkinInfo = facep->mSkinInfo;
+        draw_info->mHasPBR = has_pbr;
 
         if (gltf_mat)
         {