diff --git a/libcxxabi/src/cxa_demangle.cpp b/libcxxabi/src/cxa_demangle.cpp
--- a/libcxxabi/src/cxa_demangle.cpp
+++ b/libcxxabi/src/cxa_demangle.cpp
@@ -6,6 +6,13 @@
 //
 //===----------------------------------------------------------------------===//
 
+#if defined(__powerpc__) && \
+    (!defined(__LONG_DOUBLE_128__) || defined(__LONG_DOUBLE_IEEE128__))
+#error "Demangler must be built in double-double long double 128 mode on PPC."
+#elif defined(__s390__) && !defined(__LONG_DOUBLE_128__)
+#error "Demangler must be built in long double 128 mode on S390."
+#endif
+
 // FIXME: (possibly) incomplete list of features that clang mangles that this
 // file does not yet support:
 //   - C++ modules TS
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
@@ -3789,10 +3789,16 @@
   case 'e':
     ++First;
     return make<NameType>("long double");
-  //                ::= g    # __float128
+  //                ::= g    # long double, __float128
+#if defined(__powerpc__) || defined(__s390__)
+  case 'g':
+    ++First;
+    return make<NameType>("long double");
+#else
   case 'g':
     ++First;
     return make<NameType>("__float128");
+#endif
   //                ::= z    # ellipsis
   case 'z':
     ++First;
@@ -4223,9 +4229,18 @@
   case 'd':
     ++First;
     return getDerived().template parseFloatingLiteral<double>();
+#if defined(__powerpc__) || defined(__s390__)
+  case 'e':
+    ++First;
+    return getDerived().template parseFloatingLiteral<double>();
+  case 'g':
+    ++First;
+    return getDerived().template parseFloatingLiteral<long double>();
+#else
   case 'e':
     ++First;
     return getDerived().template parseFloatingLiteral<long double>();
+#endif
   case '_':
     if (consumeIf("_Z")) {
       Node *R = getDerived().parseEncoding();
@@ -5167,7 +5182,7 @@
 struct FloatData<long double>
 {
 #if defined(__mips__) && defined(__mips_n64) || defined(__aarch64__) || \
-    defined(__wasm__)
+    defined(__wasm__) || defined(__powerpc__) || defined(__s390__)
     static const size_t mangled_size = 32;
 #elif defined(__arm__) || defined(__mips__) || defined(__hexagon__)
     static const size_t mangled_size = 16;