diff --git a/src/compiler/translator/ParseContext.cpp b/src/compiler/translator/ParseContext.cpp
index 75828189cd..787ff9f75b 100644
--- a/src/compiler/translator/ParseContext.cpp
+++ b/src/compiler/translator/ParseContext.cpp
@@ -7087,6 +7087,22 @@ TIntermTyped *TParseContext::addIndexExpression(TIntermTyped *baseExpression,
                                         "[]");
                         safeIndex = 0;
                     }
+                    // When EXT_blend_func_extended is enabled, gl_FragData (and its
+                    // backend replacement webgl_FragData) is sized to
+                    // MaxDualSourceDrawBuffers, not MaxDrawBuffers (see
+                    // EmulateFragColorData / TranslatorGLSL). Enforce that bound here so
+                    // we never emit an OOB constant index into the shrunk array to the
+                    // native driver.
+                    else if (isExtensionEnabled(TExtension::EXT_blend_func_extended) &&
+                             index >= mResources.MaxDualSourceDrawBuffers)
+                    {
+                        outOfRangeError(outOfRangeIndexIsError, location,
+                                        "array index for gl_FragData must be less than "
+                                        "GL_MAX_DUAL_SOURCE_DRAW_BUFFERS_EXT when "
+                                        "GL_EXT_blend_func_extended is enabled",
+                                        "[]");
+                        safeIndex = mResources.MaxDualSourceDrawBuffers - 1;
+                    }
                 }
             }
             // Only do generic out-of-range check if similar error hasn't already been reported.