diff --git a/libc/src/__support/CPP/TypeTraits.h b/libc/src/__support/CPP/TypeTraits.h
--- a/libc/src/__support/CPP/TypeTraits.h
+++ b/libc/src/__support/CPP/TypeTraits.h
@@ -49,8 +49,11 @@
       IsSameV<unsigned short, TypeNoCV> || IsSameV<int, TypeNoCV> ||
       IsSameV<unsigned int, TypeNoCV> || IsSameV<long, TypeNoCV> ||
       IsSameV<unsigned long, TypeNoCV> || IsSameV<long long, TypeNoCV> ||
-      IsSameV<unsigned long long, TypeNoCV> || IsSameV<bool, TypeNoCV> ||
-      IsSameV<__uint128_t, TypeNoCV> || IsSameV<__int128_t, TypeNoCV>;
+      IsSameV<unsigned long long, TypeNoCV> || IsSameV<bool, TypeNoCV>
+#ifdef __SIZEOF_INT128__
+      || IsSameV<__uint128_t, TypeNoCV> || IsSameV<__int128_t, TypeNoCV>
+#endif
+      ;
 };
 
 template <typename T> struct IsPointerTypeNoCV : public FalseValue {};
diff --git a/libc/src/__support/FPUtil/PlatformDefs.h b/libc/src/__support/FPUtil/PlatformDefs.h
--- a/libc/src/__support/FPUtil/PlatformDefs.h
+++ b/libc/src/__support/FPUtil/PlatformDefs.h
@@ -15,8 +15,10 @@
 #define X87_FPU
 #endif
 
+// https://developer.arm.com/documentation/dui0491/i/C-and-C---Implementation-Details/Basic-data-types
 // https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms
-#if defined(_WIN32) || (defined(__APPLE__) && defined(__aarch64__))
+#if defined(_WIN32) || defined(__arm__) ||                                     \
+    (defined(__APPLE__) && defined(__aarch64__))
 #define LONG_DOUBLE_IS_DOUBLE
 #endif
 
diff --git a/libc/utils/UnitTest/LibcTest.cpp b/libc/utils/UnitTest/LibcTest.cpp
--- a/libc/utils/UnitTest/LibcTest.cpp
+++ b/libc/utils/UnitTest/LibcTest.cpp
@@ -42,6 +42,7 @@
 
 std::string describeValue(std::string Value) { return std::string(Value); }
 
+#ifdef __SIZEOF_INT128__
 // When the value is __uint128_t, also show its hexadecimal digits.
 // Using template to force exact match, prevent ambiguous promotion.
 std::string describeValue128(__uint128_t Value) {
@@ -61,6 +62,7 @@
 template <> std::string describeValue<__uint128_t>(__uint128_t Value) {
   return describeValue128(Value);
 }
+#endif
 
 template <typename ValType>
 void explainDifference(ValType LHS, ValType RHS, const char *LHSStr,
@@ -218,10 +220,12 @@
                               const char *RHSStr, const char *File,
                               unsigned long Line);
 
+#ifdef __SIZEOF_INT128__
 template bool test<__int128_t>(RunContext *Ctx, TestCondition Cond,
                                __int128_t LHS, __int128_t RHS,
                                const char *LHSStr, const char *RHSStr,
                                const char *File, unsigned long Line);
+#endif
 
 template bool test<unsigned char>(RunContext *Ctx, TestCondition Cond,
                                   unsigned char LHS, unsigned char RHS,
@@ -253,10 +257,12 @@
                                        const char *LHSStr, const char *RHSStr,
                                        const char *File, unsigned long Line);
 
+#ifdef __SIZEOF_INT128__
 template bool test<__uint128_t>(RunContext *Ctx, TestCondition Cond,
                                 __uint128_t LHS, __uint128_t RHS,
                                 const char *LHSStr, const char *RHSStr,
                                 const char *File, unsigned long Line);
+#endif
 
 } // namespace internal