diff --git a/libcxxabi/src/demangle/ItaniumDemangle.h b/libcxxabi/src/demangle/ItaniumDemangle.h
--- a/libcxxabi/src/demangle/ItaniumDemangle.h
+++ b/libcxxabi/src/demangle/ItaniumDemangle.h
@@ -5099,7 +5099,7 @@
 struct FloatData<long double>
 {
 #if defined(__mips__) && defined(__mips_n64) || defined(__aarch64__) || \
-    defined(__wasm__)
+    defined(__wasm__) || defined(__riscv)
     static const size_t mangled_size = 32;
 #elif defined(__arm__) || defined(__mips__) || defined(__hexagon__)
     static const size_t mangled_size = 16;
diff --git a/llvm/include/llvm/Demangle/ItaniumDemangle.h b/llvm/include/llvm/Demangle/ItaniumDemangle.h
--- a/llvm/include/llvm/Demangle/ItaniumDemangle.h
+++ b/llvm/include/llvm/Demangle/ItaniumDemangle.h
@@ -5099,7 +5099,7 @@
 struct FloatData<long double>
 {
 #if defined(__mips__) && defined(__mips_n64) || defined(__aarch64__) || \
-    defined(__wasm__)
+    defined(__wasm__) || defined(__riscv)
     static const size_t mangled_size = 32;
 #elif defined(__arm__) || defined(__mips__) || defined(__hexagon__)
     static const size_t mangled_size = 16;