diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc
index 73e739c503ddd1f9df1e6fc21682374024f5236a..aae5726009798a9fd27fced23e420a7ad25e335d 100644
--- a/gcc/c-family/c-common.cc
+++ b/gcc/c-family/c-common.cc
@@ -2739,7 +2739,9 @@ c_common_signed_or_unsigned_type (int unsignedp, tree type)
       || TYPE_UNSIGNED (type) == unsignedp)
     return type;
 
-  if (TREE_CODE (type) == BITINT_TYPE)
+  if (TREE_CODE (type) == BITINT_TYPE
+      /* signed _BitInt(1) is invalid, avoid creating that.  */
+      && (unsignedp || TYPE_PRECISION (type) > 1))
     return build_bitint_type (TYPE_PRECISION (type), unsignedp);
 
 #define TYPE_OK(node)							    \
diff --git a/gcc/tree.cc b/gcc/tree.cc
index b34d75f8c85c322a2bb19a9a414d0c50cbf04e4d..8a8d6d5091a403c0888e81f9c16204643b3c9a19 100644
--- a/gcc/tree.cc
+++ b/gcc/tree.cc
@@ -7179,6 +7179,8 @@ build_bitint_type (unsigned HOST_WIDE_INT precision, int unsignedp)
 {
   tree itype, ret;
 
+  gcc_checking_assert (precision >= 1 + !unsignedp);
+
   if (unsignedp)
     unsignedp = MAX_INT_CACHED_PREC + 1;
 
@@ -11096,7 +11098,7 @@ signed_or_unsigned_type_for (int unsignedp, tree type)
   else
     return NULL_TREE;
 
-  if (TREE_CODE (type) == BITINT_TYPE)
+  if (TREE_CODE (type) == BITINT_TYPE && (unsignedp || bits > 1))
     return build_bitint_type (bits, unsignedp);
   return build_nonstandard_integer_type (bits, unsignedp);
 }