diff --git a/src/gpu/gl/builders/GrGLProgramBuilder.cpp b/src/gpu/gl/builders/GrGLProgramBuilder.cpp
index 8fb3589..dd982b9 100644
--- a/src/gpu/gl/builders/GrGLProgramBuilder.cpp
+++ b/src/gpu/gl/builders/GrGLProgramBuilder.cpp
@@ -154,6 +154,8 @@
     settings.fCaps = this->gpu()->glCaps().shaderCaps();
     settings.fFlipY = this->pipeline().proxy()->origin() != kTopLeft_GrSurfaceOrigin;
     settings.fSharpenTextures = this->gpu()->getContext()->contextPriv().sharpenMipmappedTextures();
+    settings.fFragColorIsInOut = this->fragColorIsInOut();
+
     SkSL::Program::Inputs inputs;
     SkTDArray<GrGLuint> shadersToDelete;
     bool cached = fGpu->glCaps().programBinarySupport() && nullptr != fCached.get();
diff --git a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp
index 8ad3a05..9afd470 100644
--- a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp
+++ b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp
@@ -170,6 +170,11 @@
     return fHasCustomColorOutput ? DeclaredColorOutputName() : "sk_FragColor";
 }
 
+bool GrGLSLFragmentShaderBuilder::primaryColorOutputIsInOut() const {
+    return fHasCustomColorOutput &&
+           fOutputs[fCustomColorOutputIndex].getTypeModifier() == GrShaderVar::kInOut_TypeModifier;
+}
+
 void GrGLSLFragmentBuilder::declAppendf(const char* fmt, ...) {
     va_list argp;
     va_start(argp, fmt);
diff --git a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
index 5a73c17..0e0794f 100644
--- a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
+++ b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
@@ -119,6 +119,7 @@
     void enableSecondaryOutput();
     const char* getPrimaryColorOutputName() const;
     const char* getSecondaryColorOutputName() const;
+    bool primaryColorOutputIsInOut() const;
 
 #ifdef SK_DEBUG
     // As GLSLProcessors emit code, there are some conditions we need to verify.  We use the below
diff --git a/src/gpu/glsl/GrGLSLProgramBuilder.h b/src/gpu/glsl/GrGLSLProgramBuilder.h
index ac2d496..d4d2099 100644
--- a/src/gpu/glsl/GrGLSLProgramBuilder.h
+++ b/src/gpu/glsl/GrGLSLProgramBuilder.h
@@ -115,6 +115,8 @@
 
     void finalizeShaders();
 
+    bool fragColorIsInOut() const { return fFS.primaryColorOutputIsInOut(); }
+
 private:
     // reset is called by program creator between each processor's emit code.  It increments the
     // stage offset for variable name mangling, and also ensures verfication variables in the
diff --git a/src/gpu/vk/GrVkPipelineStateBuilder.cpp b/src/gpu/vk/GrVkPipelineStateBuilder.cpp
index a263b77..392c152 100644
--- a/src/gpu/vk/GrVkPipelineStateBuilder.cpp
+++ b/src/gpu/vk/GrVkPipelineStateBuilder.cpp
@@ -144,6 +144,7 @@
     settings.fCaps = this->caps()->shaderCaps();
     settings.fFlipY = this->pipeline().proxy()->origin() != kTopLeft_GrSurfaceOrigin;
     settings.fSharpenTextures = this->gpu()->getContext()->contextPriv().sharpenMipmappedTextures();
+    SkASSERT(!this->fragColorIsInOut());
     SkAssertResult(this->createVkShaderModule(VK_SHADER_STAGE_VERTEX_BIT,
                                               fVS,
                                               &vertShaderModule,
diff --git a/src/sksl/SkSLGLSLCodeGenerator.cpp b/src/sksl/SkSLGLSLCodeGenerator.cpp
index 996714e..43c1c95 100644
--- a/src/sksl/SkSLGLSLCodeGenerator.cpp
+++ b/src/sksl/SkSLGLSLCodeGenerator.cpp
@@ -1270,7 +1270,11 @@
                     this->writeLine();
                 } else if (builtin == SK_FRAGCOLOR_BUILTIN &&
                            fProgram.fSettings.fCaps->mustDeclareFragmentShaderOutput()) {
-                    this->write("out ");
+                    if (fProgram.fSettings.fFragColorIsInOut) {
+                        this->write("inout ");
+                    } else {
+                        this->write("out ");
+                    }
                     if (usesPrecisionModifiers()) {
                         this->write("mediump ");
                     }
diff --git a/src/sksl/SkSLMetalCodeGenerator.cpp b/src/sksl/SkSLMetalCodeGenerator.cpp
index de6b1d0..a8301c2 100644
--- a/src/sksl/SkSLMetalCodeGenerator.cpp
+++ b/src/sksl/SkSLMetalCodeGenerator.cpp
@@ -451,6 +451,8 @@
     }
     this->writeLine(") {");
 
+    ASSERT(!fProgram.fSettings.fFragColorIsInOut);
+
     if ("main" == f.fDeclaration.fName) {
         switch (fProgram.fKind) {
             case Program::kFragment_Kind:
diff --git a/src/sksl/SkSLSPIRVCodeGenerator.cpp b/src/sksl/SkSLSPIRVCodeGenerator.cpp
index dadab91..5f312af 100644
--- a/src/sksl/SkSLSPIRVCodeGenerator.cpp
+++ b/src/sksl/SkSLSPIRVCodeGenerator.cpp
@@ -2545,6 +2545,7 @@
         }
         if (var->fModifiers.fLayout.fBuiltin == SK_FRAGCOLOR_BUILTIN &&
             kind != Program::kFragment_Kind) {
+            ASSERT(!fProgram.fSettings.fFragColorIsInOut);
             continue;
         }
         if (!var->fReadCount && !var->fWriteCount &&
diff --git a/src/sksl/ir/SkSLProgram.h b/src/sksl/ir/SkSLProgram.h
index cbb9dfe..03a94fa 100644
--- a/src/sksl/ir/SkSLProgram.h
+++ b/src/sksl/ir/SkSLProgram.h
@@ -71,6 +71,8 @@
         // if false, sk_FragCoord is exactly the same as gl_FragCoord. If true, the y coordinate
         // must be flipped.
         bool fFlipY = false;
+        // If true the destination fragment color is read sk_FragColor. It must be declared inout.
+        bool fFragColorIsInOut = false;
         // if true, Setting objects (e.g. sk_Caps.fbFetchSupport) should be replaced with their
         // constant equivalents during compilation
         bool fReplaceSettings = true;