diff --git a/flang/lib/Lower/CallInterface.cpp b/flang/lib/Lower/CallInterface.cpp
--- a/flang/lib/Lower/CallInterface.cpp
+++ b/flang/lib/Lower/CallInterface.cpp
@@ -880,8 +880,11 @@
       addMLIRAttr(fir::getContiguousAttrName());
     if (obj.attrs.test(Attrs::Value))
       isValueAttr = true; // TODO: do we want an mlir::Attribute as well?
-    if (obj.attrs.test(Attrs::Volatile))
-      TODO(loc, "VOLATILE in procedure interface");
+    if (obj.attrs.test(Attrs::Volatile)) {
+      mlir::emitWarning(loc,
+                        "VOLATILE keyword is not yet supported so this may "
+                        "lead to undefined behavior.");
+    }
     if (obj.attrs.test(Attrs::Target))
       addMLIRAttr(fir::getTargetAttrName());