diff --git a/src/glsl/glsl_parser_extras.cpp b/src/glsl/glsl_parser_extras.cpp
index 0b53232e9e7..7f8d47ce9bc 100644
--- a/src/glsl/glsl_parser_extras.cpp
+++ b/src/glsl/glsl_parser_extras.cpp
@@ -114,6 +114,9 @@ _mesa_glsl_parse_state::_mesa_glsl_parse_state(struct gl_context *ctx,
    }
 
    this->supported_version_string = supported;
+
+   if (ctx->Const.ForceGLSLExtensionsWarn)
+      _mesa_glsl_process_extension("all", NULL, "warn", NULL, this);
 }
 
 const char *
diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
index bce5de23823..b86aeb6c1f1 100644
--- a/src/mesa/main/mtypes.h
+++ b/src/mesa/main/mtypes.h
@@ -2772,6 +2772,12 @@ struct gl_constants
 
    GLuint GLSLVersion;  /**< GLSL version supported (ex: 120 = 1.20) */
 
+   /**
+    * Changes default GLSL extension behavior from "error" to "warn".  It's out
+    * of spec, but it can make some apps work that otherwise wouldn't.
+    */
+   GLboolean ForceGLSLExtensionsWarn;
+
    /**
     * Does the driver support real 32-bit integers?  (Otherwise, integers are
     * simulated via floats.)