diff --git a/third_party/angle/src/compiler/translator/ParseContext.cpp b/third_party/angle/src/compiler/translator/ParseContext.cpp
index ef8d290e85..c8bfda94e5 100644
--- a/third_party/angle/src/compiler/translator/ParseContext.cpp
+++ b/third_party/angle/src/compiler/translator/ParseContext.cpp
@@ -9129,6 +9129,15 @@ TIntermTyped *TParseContext::addComma(TIntermTyped *left,
     {
         error(loc, "sequence operator is not allowed for interface blocks", ",");
     }
+    // Opaque types (samplers, images, atomic counters, pixel-local-storage handles, etc.)
+    // are not allowed as operands to the sequence operator.  Without this check a
+    // pixelLocalANGLE-typed comma expression can survive to MonomorphizeUnsupportedFunctions
+    // and reach RewritePixelLocalStorage with an unbound function parameter, causing a
+    // past-the-end std::map iterator dereference.
+    if (IsOpaqueType(left->getBasicType()) || IsOpaqueType(right->getBasicType()))
+    {
+        error(loc, "sequence operator is not allowed for variables with an opaque type", ",");
+    }
 
     TIntermBinary *commaNode = TIntermBinary::CreateComma(left, right, mShaderVersion);
     markStaticUseIfSymbol(left);