diff --git a/gcc/c/ChangeLog b/gcc/c/ChangeLog
index 076a9a26501..c8e5e1a6b0b 100644
--- a/gcc/c/ChangeLog
+++ b/gcc/c/ChangeLog
@@ -1,3 +1,10 @@
+2019-04-12  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c/89933
+	* c-decl.c (merge_decls): When newdecl's type is its main variant,
+	don't try to remove it from the variant list, but instead assert
+	it has no variants.
+
 2019-04-01  Richard Biener  <rguenther@suse.de>
 
 	PR c/71598
diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
index 8d5c35ab475..ef9b874f997 100644
--- a/gcc/c/c-decl.c
+++ b/gcc/c/c-decl.c
@@ -2512,13 +2512,16 @@ merge_decls (tree newdecl, tree olddecl, tree newtype, tree oldtype)
       if (TYPE_NAME (TREE_TYPE (newdecl)) == newdecl)
 	{
 	  tree remove = TREE_TYPE (newdecl);
-	  for (tree t = TYPE_MAIN_VARIANT (remove); ;
-	       t = TYPE_NEXT_VARIANT (t))
-	    if (TYPE_NEXT_VARIANT (t) == remove)
-	      {
-		TYPE_NEXT_VARIANT (t) = TYPE_NEXT_VARIANT (remove);
-		break;
-	      }
+	  if (TYPE_MAIN_VARIANT (remove) == remove)
+	    gcc_assert (TYPE_NEXT_VARIANT (remove) == NULL_TREE);
+	  else
+	    for (tree t = TYPE_MAIN_VARIANT (remove); ;
+		 t = TYPE_NEXT_VARIANT (t))
+	      if (TYPE_NEXT_VARIANT (t) == remove)
+		{
+		  TYPE_NEXT_VARIANT (t) = TYPE_NEXT_VARIANT (remove);
+		  break;
+		}
 	}
     }
 
diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 212318e0966..67baed6672f 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,10 @@
+2019-04-12  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c/89933
+	* decl.c (duplicate_decls): When newdecl's type is its main variant,
+	don't try to remove it from the variant list, but instead assert
+	it has no variants.
+
 2019-04-12  Martin Sebor  <msebor@redhat.com>
 
 	PR c/88383
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 2528a8cd670..67d9244c450 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -2132,13 +2132,16 @@ next_arg:;
 	  if (TYPE_NAME (TREE_TYPE (newdecl)) == newdecl)
 	    {
 	      tree remove = TREE_TYPE (newdecl);
-	      for (tree t = TYPE_MAIN_VARIANT (remove); ;
-		   t = TYPE_NEXT_VARIANT (t))
-		if (TYPE_NEXT_VARIANT (t) == remove)
-		  {
-		    TYPE_NEXT_VARIANT (t) = TYPE_NEXT_VARIANT (remove);
-		    break;
-		  }
+	      if (TYPE_MAIN_VARIANT (remove) == remove)
+		gcc_assert (TYPE_NEXT_VARIANT (remove) == NULL_TREE);
+	      else
+		for (tree t = TYPE_MAIN_VARIANT (remove); ;
+		     t = TYPE_NEXT_VARIANT (t))
+		  if (TYPE_NEXT_VARIANT (t) == remove)
+		    {
+		      TYPE_NEXT_VARIANT (t) = TYPE_NEXT_VARIANT (remove);
+		      break;
+		    }
 	    }
 	}
       else if (merge_attr)
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index ed6f731b5b5..2951fc82167 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2019-04-12  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c/89933
+	* c-c++-common/pr89933.c: New test.
+
 2019-04-12  Martin Sebor  <msebor@redhat.com>
 
 	PR c/88383
diff --git a/gcc/testsuite/c-c++-common/pr89933.c b/gcc/testsuite/c-c++-common/pr89933.c
new file mode 100644
index 00000000000..870504d4208
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr89933.c
@@ -0,0 +1,5 @@
+/* PR c/89933 */
+/* { dg-do compile } */
+
+typedef unsigned int a __attribute__ ((__aligned__(8), __may_alias__));
+typedef unsigned int a __attribute__ ((__aligned__(8), __may_alias__));