diff --git a/gcc/c-family/c-attribs.cc b/gcc/c-family/c-attribs.cc
index 111a33f405ac11344e422b6362b2a623d9d50f89..b1953a45f9bb70ab1e05a97c38d32fad0398133e 100644
--- a/gcc/c-family/c-attribs.cc
+++ b/gcc/c-family/c-attribs.cc
@@ -2199,7 +2199,21 @@ handle_mode_attribute (tree *node, tree name, tree args,
 	  return NULL_TREE;
 	}
 
-      *node = build_qualified_type (typefm, TYPE_QUALS (type));
+      /* Copy any quals and attributes to the new type.  */
+      *node = build_type_attribute_qual_variant (typefm, TYPE_ATTRIBUTES (type),
+						 TYPE_QUALS (type));
+      if (TYPE_USER_ALIGN (type))
+	*node = build_aligned_type (*node, TYPE_ALIGN (type));
+
+      tree decl = node[2];
+      if (decl && TYPE_NAME (type) == decl)
+	{
+	  /* Set up the typedef all over again.  */
+	  DECL_ORIGINAL_TYPE (decl) = NULL_TREE;
+	  TREE_TYPE (decl) = *node;
+	  set_underlying_type (decl);
+	  *node = TREE_TYPE (decl);
+	}
     }
 
   return NULL_TREE;
diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc
index bb0544eeaea798c786cb2aafd62275a172d2a63b..730faa9e87f5e959c80dd7e0d1c9ca20ae15aa76 100644
--- a/gcc/c-family/c-common.cc
+++ b/gcc/c-family/c-common.cc
@@ -8153,15 +8153,16 @@ check_missing_format_attribute (tree ltype, tree rtype)
 void
 set_underlying_type (tree x)
 {
-  if (x == error_mark_node)
+  if (x == error_mark_node || TREE_TYPE (x) == error_mark_node)
     return;
   if (DECL_IS_UNDECLARED_BUILTIN (x) && TREE_CODE (TREE_TYPE (x)) != ARRAY_TYPE)
     {
       if (TYPE_NAME (TREE_TYPE (x)) == 0)
 	TYPE_NAME (TREE_TYPE (x)) = x;
     }
-  else if (TREE_TYPE (x) != error_mark_node
-	   && DECL_ORIGINAL_TYPE (x) == NULL_TREE)
+  else if (DECL_ORIGINAL_TYPE (x))
+    gcc_checking_assert (TYPE_NAME (TREE_TYPE (x)) == x);
+  else
     {
       tree tt = TREE_TYPE (x);
       DECL_ORIGINAL_TYPE (x) = tt;
diff --git a/gcc/testsuite/c-c++-common/attr-mode-1.c b/gcc/testsuite/c-c++-common/attr-mode-1.c
new file mode 100644
index 0000000000000000000000000000000000000000..04a2431f5e51c14f217eded2937b5004cd2b4ab6
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attr-mode-1.c
@@ -0,0 +1,4 @@
+// PR c/100545
+// { dg-additional-options -g }
+
+typedef int fatp_t __attribute__((aligned, mode(SI)));
diff --git a/gcc/testsuite/c-c++-common/attr-mode-2.c b/gcc/testsuite/c-c++-common/attr-mode-2.c
new file mode 100644
index 0000000000000000000000000000000000000000..de65f49c6b60c3ab86e45ef145477e86ba54c6ce
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attr-mode-2.c
@@ -0,0 +1,4 @@
+typedef int I;
+int x;
+I y __attribute__ ((mode(QI)));
+extern I x;