diff --git a/gcc/fortran/interface.c b/gcc/fortran/interface.c
index e7f1878..17f544e 100644
--- a/gcc/fortran/interface.c
+++ b/gcc/fortran/interface.c
@@ -495,6 +495,17 @@ compare_components (gfc_component *cmp1, gfc_component *cmp2,
   if (cmp1->attr.dimension && gfc_compare_array_spec (cmp1->as, cmp2->as) == 0)
     return 0;
 
+  if (cmp1->ts.type == BT_CHARACTER && cmp2->ts.type == BT_CHARACTER)
+    {
+      gfc_charlen *l1 = cmp1->ts.u.cl;
+      gfc_charlen *l2 = cmp2->ts.u.cl;
+      if (l1 && l2 && l1->length && l2->length
+          && l1->length->expr_type == EXPR_CONSTANT
+          && l2->length->expr_type == EXPR_CONSTANT
+          && gfc_dep_compare_expr (l1->length, l2->length) != 0)
+        return 0;
+    }
+
   /* Make sure that link lists do not put this function into an
      endless recursive loop!  */
   if (!(cmp1->ts.type == BT_DERIVED && derived1 == cmp1->ts.u.derived)
diff --git a/gcc/testsuite/gfortran.dg/dec_union_11.f90 b/gcc/testsuite/gfortran.dg/dec_union_11.f90
new file mode 100644
index 0000000..3ff4b49
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/dec_union_11.f90
@@ -0,0 +1,63 @@
+! { dg-do compile }
+! { dg-options "-g -fdec-structure" }
+!
+! Test a regression where typespecs of unions containing character buffers of
+! different lengths where copied, resulting in a bad gimple tree state.
+!
+
+subroutine sub2 (otherbuf)
+  integer, parameter :: L_bbuf = 65536
+  integer, parameter :: L_bbuf2 = 24
+
+  structure /buffer2/
+    union
+     map
+      character(L_bbuf2)  sbuf
+     end map
+    end union
+  end structure
+  structure /buffer/
+    union
+     map
+      character(L_bbuf)  sbuf
+     end map
+    end union
+  end structure
+
+  record /buffer/ buf1
+  record /buffer2/ buf2
+  common /c/ buf1, buf2
+
+  record /buffer2/ otherbuf
+end subroutine
+
+subroutine sub()
+  integer, parameter :: L_bbuf = 65536
+  integer, parameter :: L_bbuf2 = 24
+
+  structure /buffer2/
+    union
+     map
+      character(L_bbuf2)  sbuf
+     end map
+    end union
+  end structure
+  structure /buffer/
+    union
+     map
+      character(L_bbuf)  sbuf
+     end map
+    end union
+  end structure
+
+  record /buffer/ buf1
+  record /buffer2/ buf2
+  common /c/ buf1, buf2
+
+  call sub2 (buf1) ! { dg-warning "Type mismatch" }
+  return
+end subroutine
+
+call sub()
+
+end