Index: flang/lib/Semantics/check-declarations.cpp
===================================================================
--- flang/lib/Semantics/check-declarations.cpp
+++ flang/lib/Semantics/check-declarations.cpp
@@ -428,6 +428,11 @@
         " of a module"_err_en_US,
         symbol.name());
   }
+  if (symbol.attrs().test(Attr::ASYNCHRONOUS) &&
+      !evaluate::IsVariable(symbol)) {
+    messages_.Say(
+        "An entity may not have the ASYNCHRONOUS attribute unless it is a variable"_err_en_US);
+  }
 }
 
 void CheckHelper::CheckCommonBlock(const Symbol &symbol) {
Index: flang/test/Semantics/resolve20.f90
===================================================================
--- flang/test/Semantics/resolve20.f90
+++ flang/test/Semantics/resolve20.f90
@@ -53,6 +53,10 @@
   !ERROR: EXTERNAL attribute not allowed on 'bar'
   external :: bar
 
+  !ERROR: An entity may not have the ASYNCHRONOUS attribute unless it is a variable
+  asynchronous :: async
+  external :: async
+
   !ERROR: PARAMETER attribute not allowed on 'm'
   parameter(m=2)
   !ERROR: PARAMETER attribute not allowed on 'foo'