diff --git a/libc/include/endian.h b/libc/include/endian.h
new file mode 100644
index 00000000..7f9c359a
--- /dev/null
+++ b/libc/include/endian.h
@@ -0,0 +1,47 @@
+/* endian.h: Functions to convert between different byte orderings. */
+
+#ifndef _ENDIAN_H
+#define _ENDIAN_H
+
+#include <stdint.h>
+
+#define LITTLE_ENDIAN __ORDER_LITTLE_ENDIAN__
+#define BIG_ENDIAN __ORDER_BIG_ENDIAN__
+
+#define BYTE_ORDER __BYTE_ORDER__
+
+#if BYTE_ORDER == LITTLE_ENDIAN
+#define be16toh(x) __builtin_bswap16(x)
+#define be32toh(x) __builtin_bswap32(x)
+#define be64toh(x) __builtin_bswap64(x)
+
+#define htobe16(x) __builtin_bswap16(x)
+#define htobe32(x) __builtin_bswap32(x)
+#define htobe64(x) __builtin_bswap64(x)
+
+#define htole16(x) (x)
+#define htole32(x) (x)
+#define htole64(x) (x)
+
+#define le16toh(x) (x)
+#define le32toh(x) (x)
+#define le64toh(x) (x)
+#else
+#define be16toh(x) (x)
+#define be32toh(x) (x)
+#define be64toh(x) (x)
+
+#define htobe16(x) (x)
+#define htobe32(x) (x)
+#define htobe64(x) (x)
+
+#define htole16(x) __builtin_bswap16(x)
+#define htole32(x) __builtin_bswap32(x)
+#define htole64(x) __builtin_bswap64(x)
+
+#define le16toh(x) __builtin_bswap16(x)
+#define le32toh(x) __builtin_bswap32(x)
+#define le64toh(x) __builtin_bswap64(x)
+#endif
+
+#endif
diff --git a/libluna/src/SHA.cpp b/libluna/src/SHA.cpp
index 538c2c09..b0e2f8fd 100644
--- a/libluna/src/SHA.cpp
+++ b/libluna/src/SHA.cpp
@@ -7,6 +7,7 @@
  *
  */
 
+#include <endian.h>
 #include <luna/Alignment.h>
 #include <luna/Common.h>
 #include <luna/DebugLog.h>
@@ -62,7 +63,7 @@ Result<SHA256::Digest> SHA256::digest()
 
     // Add the length of the original message (in bits), this has to be big-endian.
     usize message_length = m_message.size() * 8;
-    message_length = __builtin_bswap64(message_length); // FIXME: We're assuming we're on a little-endian platform.
+    message_length = htobe64(message_length);
     TRY(message_block.append_data((const u8*)&message_length, sizeof(usize)));
 
     // The length of the message block should now be a multiple of 512 bits (64 bytes).
@@ -89,11 +90,13 @@ Result<SHA256::Digest> SHA256::digest()
 
         memcpy(message_schedule, &message_block.data()[i * 64], 64);
 
+#if BYTE_ORDER == LITTLE_ENDIAN
         for (int j = 0; j < 16; j++)
         {
-            // SHA uses big-endian. FIXME: Don't assume little-endian.
-            message_schedule[j] = __builtin_bswap32(message_schedule[j]);
+            // SHA uses big-endian.
+            message_schedule[j] = htobe32(message_schedule[j]);
         }
+#endif
 
         // Fill the rest of the message schedule.
         for (int j = 0; j < 48; j++)
@@ -150,15 +153,14 @@ Result<SHA256::Digest> SHA256::digest()
         h7 += h;
     }
 
-    // FIXME: Again, this assumes little-endian.
-    h0 = __builtin_bswap32(h0);
-    h1 = __builtin_bswap32(h1);
-    h2 = __builtin_bswap32(h2);
-    h3 = __builtin_bswap32(h3);
-    h4 = __builtin_bswap32(h4);
-    h5 = __builtin_bswap32(h5);
-    h6 = __builtin_bswap32(h6);
-    h7 = __builtin_bswap32(h7);
+    h0 = be32toh(h0);
+    h1 = be32toh(h1);
+    h2 = be32toh(h2);
+    h3 = be32toh(h3);
+    h4 = be32toh(h4);
+    h5 = be32toh(h5);
+    h6 = be32toh(h6);
+    h7 = be32toh(h7);
 
     Digest result;
     memcpy(&result.m_bytes[0], &h0, sizeof(u32));