diff --git a/flang/lib/Semantics/check-declarations.cpp b/flang/lib/Semantics/check-declarations.cpp
index 31e246cf0ab03..3e21bc6f218a7 100644
--- a/flang/lib/Semantics/check-declarations.cpp
+++ b/flang/lib/Semantics/check-declarations.cpp
@@ -1781,7 +1781,7 @@ void CheckHelper::CheckExternal(const Symbol &symbol) {
         if (auto previousChars{Characterize(previous)}) {
           std::string whyNot;
           if (!chars->IsCompatibleWith(*previousChars,
-                  /*ignoreImplicitVsExplicit=*/false, &whyNot)) {
+                  /*ignoreImplicitVsExplicit=*/true, &whyNot)) {
             if (auto *msg{Warn(common::UsageWarning::ExternalInterfaceMismatch,
                     "The external interface '%s' is not compatible with an earlier definition (%s)"_warn_en_US,
                     symbol.name(), whyNot)}) {
diff --git a/flang/test/Semantics/bug1491.f90 b/flang/test/Semantics/bug1491.f90
new file mode 100644
index 0000000000000..ccc6eea31a1d4
--- /dev/null
+++ b/flang/test/Semantics/bug1491.f90
@@ -0,0 +1,21 @@
+!RUN: %python %S/test_errors.py %s %flang_fc1 -Werror -pedantic
+module m
+  interface
+    integer function foo1()
+    end function
+    integer function foo2(j)
+    end function
+    integer function foo3()
+    end function
+  end interface
+end module
+
+subroutine test()
+  integer, external :: foo1
+!WARNING: The external interface 'foo2' is not compatible with an earlier definition (distinct numbers of dummy arguments) [-Wexternal-interface-mismatch]
+  integer, external :: foo2
+  integer, external :: foo3
+  call bar(foo1())
+  call bar(foo2())
+  call baz(foo3)
+end subroutine
diff --git a/flang/test/Semantics/null-init.f90 b/flang/test/Semantics/null-init.f90
index d01ad75a75a11..a88cefe136a5e 100644
--- a/flang/test/Semantics/null-init.f90
+++ b/flang/test/Semantics/null-init.f90
@@ -37,7 +37,7 @@ module m6
 
 module m7
   interface
-    !WARNING: The external interface 'null' is not compatible with an earlier definition (incompatible procedure attributes: ImplicitInterface) [-Wexternal-interface-mismatch]
+    !WARNING: The external interface 'null' is not compatible with an earlier definition (function results have incompatible attributes) [-Wexternal-interface-mismatch]
     function null() result(p)
       integer, pointer :: p
     end function