diff --git a/libc/src/string/memory_utils/bcmp_implementations.h b/libc/src/string/memory_utils/bcmp_implementations.h
--- a/libc/src/string/memory_utils/bcmp_implementations.h
+++ b/libc/src/string/memory_utils/bcmp_implementations.h
@@ -23,10 +23,11 @@
 #elif defined(LIBC_TARGET_ARCH_IS_ANY_RISCV)
 #include "src/string/memory_utils/riscv/bcmp_implementations.h"
 #define LIBC_SRC_STRING_MEMORY_UTILS_BCMP inline_bcmp_riscv
-#else
-// We may want to error instead of defaulting to suboptimal implementation.
+#elif defined(LIBC_TARGET_ARCH_IS_ARM) || defined(LIBC_TARGET_ARCH_IS_GPU)
 #include "src/string/memory_utils/generic/byte_per_byte.h"
 #define LIBC_SRC_STRING_MEMORY_UTILS_BCMP inline_bcmp_byte_per_byte
+#else
+#error "Unsupported architecture"
 #endif
 
 namespace __llvm_libc {
diff --git a/libc/src/string/memory_utils/memcmp_implementations.h b/libc/src/string/memory_utils/memcmp_implementations.h
--- a/libc/src/string/memory_utils/memcmp_implementations.h
+++ b/libc/src/string/memory_utils/memcmp_implementations.h
@@ -24,10 +24,11 @@
 #elif defined(LIBC_TARGET_ARCH_IS_ANY_RISCV)
 #include "src/string/memory_utils/riscv/memcmp_implementations.h"
 #define LIBC_SRC_STRING_MEMORY_UTILS_MEMCMP inline_memcmp_riscv
-#else
-// We may want to error instead of defaulting to suboptimal implementation.
+#elif defined(LIBC_TARGET_ARCH_IS_ARM) || defined(LIBC_TARGET_ARCH_IS_GPU)
 #include "src/string/memory_utils/generic/byte_per_byte.h"
 #define LIBC_SRC_STRING_MEMORY_UTILS_MEMCMP inline_memcmp_byte_per_byte
+#else
+#error "Unsupported architecture"
 #endif
 
 namespace __llvm_libc {
diff --git a/libc/src/string/memory_utils/memcpy_implementations.h b/libc/src/string/memory_utils/memcpy_implementations.h
--- a/libc/src/string/memory_utils/memcpy_implementations.h
+++ b/libc/src/string/memory_utils/memcpy_implementations.h
@@ -28,10 +28,11 @@
 #elif defined(LIBC_TARGET_ARCH_IS_ANY_RISCV)
 #include "src/string/memory_utils/riscv/memcpy_implementations.h"
 #define LIBC_SRC_STRING_MEMORY_UTILS_MEMCPY inline_memcpy_riscv
-#else
-// We may want to error instead of defaulting to suboptimal implementation.
+#elif defined(LIBC_TARGET_ARCH_IS_ARM) || defined(LIBC_TARGET_ARCH_IS_GPU)
 #include "src/string/memory_utils/generic/byte_per_byte.h"
 #define LIBC_SRC_STRING_MEMORY_UTILS_MEMCPY inline_memcpy_byte_per_byte
+#else
+#error "Unsupported architecture"
 #endif
 
 namespace __llvm_libc {
diff --git a/libc/src/string/memory_utils/memmove_implementations.h b/libc/src/string/memory_utils/memmove_implementations.h
--- a/libc/src/string/memory_utils/memmove_implementations.h
+++ b/libc/src/string/memory_utils/memmove_implementations.h
@@ -20,10 +20,11 @@
 #elif defined(LIBC_TARGET_ARCH_IS_ANY_RISCV)
 #include "src/string/memory_utils/riscv/memmove_implementations.h"
 #define LIBC_SRC_STRING_MEMORY_UTILS_MEMMOVE inline_memmove_riscv
-#else
-// We may want to error instead of defaulting to suboptimal implementation.
+#elif defined(LIBC_TARGET_ARCH_IS_ARM) || defined(LIBC_TARGET_ARCH_IS_GPU)
 #include "src/string/memory_utils/generic/byte_per_byte.h"
 #define LIBC_SRC_STRING_MEMORY_UTILS_MEMMOVE inline_memmove_byte_per_byte
+#else
+#error "Unsupported architecture"
 #endif
 
 namespace __llvm_libc {
diff --git a/libc/src/string/memory_utils/memset_implementations.h b/libc/src/string/memory_utils/memset_implementations.h
--- a/libc/src/string/memory_utils/memset_implementations.h
+++ b/libc/src/string/memory_utils/memset_implementations.h
@@ -24,10 +24,11 @@
 #elif defined(LIBC_TARGET_ARCH_IS_ANY_RISCV)
 #include "src/string/memory_utils/riscv/memset_implementations.h"
 #define LIBC_SRC_STRING_MEMORY_UTILS_MEMSET inline_memset_riscv
-#else
-// We may want to error instead of defaulting to suboptimal implementation.
+#elif defined(LIBC_TARGET_ARCH_IS_ARM) || defined(LIBC_TARGET_ARCH_IS_GPU)
 #include "src/string/memory_utils/generic/byte_per_byte.h"
 #define LIBC_SRC_STRING_MEMORY_UTILS_MEMSET inline_memset_byte_per_byte
+#else
+#error "Unsupported architecture"
 #endif
 
 namespace __llvm_libc {