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diff --git a/gcc/testsuite/gfortran.dg/do_2.f90 b/gcc/testsuite/gfortran.dg/do_2.f90
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+! { dg-do compile }
+! Check the fix for PR20839, which concerned non-compliance with one of the
+! constraints for block-do-constructs (8.1.4.1.1):
+! Constraint: If the do-stmt of a block-do-construct is identified by a 
+! do-construct-name, the corresponding end-do shall be an end-do-stmt
+! specifying the same do-construct-name. (Tests a & b)
+! If the do-stmt of a block-do-construct is not identified by a
+! do-construct-name, the corresponding end-do shall not specify a
+! do-construct-name. (Tests c & d)
+! Constraint: If the do-stmt is a nonlabel-do-stmt, the corresponding end-do
+! shall be an end-do-stmt.
+! Constraint: If the do-stmt is a label-do-stmt, the corresponding end-do shall
+! be identified with the same label.
+!
+! Test a - this was the PR
+  doi: DO 111 i=1,3 ! { dg-error "requires matching ENDDO name" }
+111 continue 
+! Test b
+  doii: DO 112 ij=1,3
+112 enddo doij      ! { dg-error "Expected label" }
+! Test c
+  DO 113 ik=1,3
+113 enddo doik      ! { dg-error "Syntax error" }
+! Test d
+  DO il=1,3
+  enddo doil        ! { dg-error "Syntax error" }
+! Test e
+  doj: DO 114 j=1,3
+  enddo doj         ! { dg-error "doesn't match DO label" }
+
+! Correct block do constructs
+dok: DO 115 k=1,3
+    dokk: do kk=1,3
+        dokkk: DO
+                   do kkkk=1,3
+                       do
+                       enddo
+                   enddo
+               enddo dokkk
+          enddo dokk
+115  enddo dok 
+! Correct non-block do constructs
+  do 117 l=1,3
+      do ll=1,3
+          do 116 lll=1,3
+116       continue
+      enddo
+117 enddo
+! These prevent an EOF error, arising from the previous errors.
+end do
+113 end do
+112 end do doii
+END
+