diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 793e4afffcb..11acab7008e 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,15 @@
+2020-02-14  Jakub Jelinek  <jakub@redhat.com>
+
+	PR libstdc++/92906
+	* cp-tree.h (enum cp_tree_index): Add CPTI_FALLBACK_DFLOAT32_TYPE,
+	CPTI_FALLBACK_DFLOAT64_TYPE and CPTI_FALLBACK_DFLOAT128_TYPE.
+	(fallback_dfloat32_type, fallback_dfloat64_type,
+	fallback_dfloat128_type): Define.
+	* mangle.c (write_builtin_type): Handle fallback_dfloat*_type like
+	dfloat*_type_node.
+	* rtti.c (emit_support_tinfos): Emit DFP typeinfos even when dfp
+	is disabled for compatibility.
+
 2020-02-13  Jason Merrill  <jason@redhat.com>
 
 	PR c++/93713
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 53de2b0afe7..c1aafa1de3a 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -206,6 +206,10 @@ enum cp_tree_index
 
     CPTI_SOURCE_LOCATION_IMPL,
 
+    CPTI_FALLBACK_DFLOAT32_TYPE,
+    CPTI_FALLBACK_DFLOAT64_TYPE,
+    CPTI_FALLBACK_DFLOAT128_TYPE,
+
     CPTI_MAX
 };
 
@@ -366,6 +370,12 @@ extern GTY(()) tree cp_global_trees[CPTI_MAX];
 
 #define access_default_node		null_node
 
+/* Variant of dfloat{32,64,128}_type_node only used for fundamental
+   rtti purposes if DFP is disabled.  */
+#define fallback_dfloat32_type		cp_global_trees[CPTI_FALLBACK_DFLOAT32_TYPE]
+#define fallback_dfloat64_type		cp_global_trees[CPTI_FALLBACK_DFLOAT64_TYPE]
+#define fallback_dfloat128_type		cp_global_trees[CPTI_FALLBACK_DFLOAT128_TYPE]
+
 
 #include "name-lookup.h"
 
diff --git a/gcc/cp/mangle.c b/gcc/cp/mangle.c
index 23baa382ed9..a0e888fde62 100644
--- a/gcc/cp/mangle.c
+++ b/gcc/cp/mangle.c
@@ -2569,11 +2569,11 @@ write_builtin_type (tree type)
 	write_char ('d');
       else if (type == long_double_type_node)
 	write_char ('e');
-      else if (type == dfloat32_type_node)
+      else if (type == dfloat32_type_node || type == fallback_dfloat32_type)
 	write_string ("Df");
-      else if (type == dfloat64_type_node)
+      else if (type == dfloat64_type_node || type == fallback_dfloat64_type)
 	write_string ("Dd");
-      else if (type == dfloat128_type_node)
+      else if (type == dfloat128_type_node || type == fallback_dfloat128_type)
 	write_string ("De");
       else
 	gcc_unreachable ();
diff --git a/gcc/cp/rtti.c b/gcc/cp/rtti.c
index 36c1b4ed7bc..f20941c413b 100644
--- a/gcc/cp/rtti.c
+++ b/gcc/cp/rtti.c
@@ -1588,6 +1588,20 @@ emit_support_tinfos (void)
       }
   for (tree t = registered_builtin_types; t; t = TREE_CHAIN (t))
     emit_support_tinfo_1 (TREE_VALUE (t));
+  /* For compatibility, emit DFP typeinfos even when DFP isn't enabled,
+     because we've emitted that in the past.  */
+  if (!targetm.decimal_float_supported_p ())
+    {
+      gcc_assert (dfloat32_type_node == NULL_TREE
+		  && dfloat64_type_node == NULL_TREE
+		  && dfloat128_type_node == NULL_TREE);
+      fallback_dfloat32_type = make_node (REAL_TYPE);
+      fallback_dfloat64_type = make_node (REAL_TYPE);
+      fallback_dfloat128_type = make_node (REAL_TYPE);
+      emit_support_tinfo_1 (fallback_dfloat32_type);
+      emit_support_tinfo_1 (fallback_dfloat64_type);
+      emit_support_tinfo_1 (fallback_dfloat128_type);
+    }
   input_location = saved_loc;
 }