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diff --git a/gcc/testsuite/gfortran.dg/interface_3.f90 b/gcc/testsuite/gfortran.dg/interface_3.f90
new file mode 100644
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+++ b/gcc/testsuite/gfortran.dg/interface_3.f90
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+! { dg-do compile }
+! Tests the fix for PR20880, which was due to failure to the failure
+! to detect the USE association of a nameless interface for a
+! procedure with the same name as the encompassing scope.
+!
+! Contributed by Joost VandeVondele  <jv244@cam.ac.uk>
+!
+module test_mod
+interface
+  subroutine my_sub (a)
+    real a
+  end subroutine
+end interface
+interface
+  function my_fun (a)
+    real a, my_fun
+  end function
+end interface
+end module
+
+! This is the original PR
+subroutine my_sub (a) ! { dg-error "is ambiguous" }
+  use test_mod
+  real a
+  print *, a
+end subroutine
+
+integer function my_fun (a) ! { dg-error "is ambiguous" }
+  use test_mod
+  real a
+  print *, a
+  my_fun = 1  ! { dg-error "ambiguous reference" }
+end function
+
+! This was found whilst investigating => segfault
+subroutine thy_sub (a)
+  interface 
+    subroutine thy_sub (a) ! { dg-error "enclosing procedure" }
+      real a
+    end subroutine
+  end interface
+  real a
+  print *, a
+end subroutine
+! { dg-final { cleanup-modules "test_mod" } }