diff --git a/.github/workflows/build-and-test-other.yaml b/.github/workflows/build-and-test-other.yaml
index 98d160c00..c7a1bcee4 100644
--- a/.github/workflows/build-and-test-other.yaml
+++ b/.github/workflows/build-and-test-other.yaml
@@ -108,11 +108,11 @@ jobs:
           tag: "bullseye"
           cflags: "-O2"
 
-        # It looks like we don't really support big-endian
-        # - arch: "powerpc"
-        #  distro: "jessie"
-        #  base_url: "http://archive.debian.org/debian"
-        #  cflags: "-std=gnu99 -Os"
+        # Required for testing big endian archs
+        - arch: "s390x"
+          platform: "s390x"
+          tag: "bullseye"
+          cflags: "-O2"
 
     steps:
     - name: Checkout repo
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5b8a59954..d347ee58c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Fixed a bug where guards would raise exceptions instead of just being false
+- Fixed support for big endian CPUs (such as some MIPS CPUs).
 
 ## [0.6.0-alpha.1] - 2023-10-09
 
diff --git a/src/libAtomVM/iff.c b/src/libAtomVM/iff.c
index 374a94503..6bb2c428c 100644
--- a/src/libAtomVM/iff.c
+++ b/src/libAtomVM/iff.c
@@ -53,7 +53,9 @@ void scan_iff(const void *iff_binary, int buf_size, unsigned long *offsets, unsi
     uint32_t iff_size = READ_32_ALIGNED(data + 4);
     int file_size = iff_size;
     if (UNLIKELY(buf_size < file_size)) {
-        fprintf(stderr, "warning: buffer holding IFF is smaller than IFF size: %i", buf_size);
+        fprintf(stderr, "error: buffer holding IFF is smaller than IFF size: %i\n", buf_size);
+        // TODO: return error instead of crashing
+        AVM_ABORT();
     }
 
     do {
diff --git a/src/libAtomVM/utils.h b/src/libAtomVM/utils.h
index 260adccfd..2d396dfa5 100644
--- a/src/libAtomVM/utils.h
+++ b/src/libAtomVM/utils.h
@@ -28,7 +28,7 @@
 #ifndef _UTILS_H_
 #define _UTILS_H_
 
-#ifdef __ORDER_LITTLE_ENDIAN__
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
     #ifdef __GNUC__
         #define READ_32_ALIGNED(ptr) \
             __builtin_bswap32(*((uint32_t *) (ptr)))
@@ -102,7 +102,26 @@
         #define ENDIAN_SWAP_32(value) ((((value) & 0xFF) << 24) | (((value) & 0xFF00) << 8) | (((value) & 0xFF0000) >> 8) | (((value) & 0xFF000000) >> 24))
     #endif
 
-#else
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+
+    #define READ_64_UNALIGNED(ptr) \
+        ( (((uint64_t) ((uint8_t *)(ptr))[0]) << 56) | (((uint64_t) ((uint8_t *) (ptr))[1]) << 48) | \
+            (((uint64_t) ((uint8_t *)(ptr))[2]) << 40) | (((uint64_t) ((uint8_t *) (ptr))[3]) << 32) | \
+            (((uint64_t) ((uint8_t *)(ptr))[4]) << 24) | (((uint64_t) ((uint8_t *) (ptr))[5]) << 16) | \
+            (((uint64_t) ((uint8_t *)(ptr))[6]) << 8) | (((uint64_t) ((uint8_t *) (ptr))[7])) )
+
+    #define WRITE_64_UNALIGNED(ptr, val) \
+        { \
+            ((uint8_t *)(ptr))[0] = (((uint64_t) val) >> 56) & 0xff; \
+            ((uint8_t *)(ptr))[1] = (((uint64_t) val) >> 48) & 0xff; \
+            ((uint8_t *)(ptr))[2] = (((uint64_t) val) >> 40) & 0xff; \
+            ((uint8_t *)(ptr))[3] = (((uint64_t) val) >> 32) & 0xff; \
+            ((uint8_t *)(ptr))[4] = (((uint64_t) val) >> 24) & 0xff; \
+            ((uint8_t *)(ptr))[5] = (((uint64_t) val) >> 16) & 0xff; \
+            ((uint8_t *)(ptr))[6] = (((uint64_t) val) >> 8) & 0xff; \
+            ((uint8_t *)(ptr))[7] = ((uint64_t) val) & 0xff; \
+        }
+
     #define READ_32_ALIGNED(ptr) \
         (*((uint32_t *) (ptr)))
 
@@ -110,15 +129,26 @@
         ( (((uint8_t *)(ptr))[0] << 24) | (((uint8_t *) (ptr))[1] << 16) | (((uint8_t *)(ptr))[2] << 8) | ((uint8_t *)(ptr))[3] )
 
     #define WRITE_32_UNALIGNED(ptr, val) \
-        *((uint32_t *) (ptr)) = ( (((uint8_t *)(&val))[0] << 24) | (((uint8_t *) (&val))[1] << 16) | (((uint8_t *)(&val))[2] << 8) | ((uint8_t *)(&val))[3] )
+        { \
+            ((uint8_t *)(ptr))[0] = (((uint32_t) val) >> 24) & 0xff; \
+            ((uint8_t *)(ptr))[1] = (((uint32_t) val) >> 16) & 0xff; \
+            ((uint8_t *)(ptr))[2] = (((uint32_t) val) >> 8) & 0xff; \
+            ((uint8_t *)(ptr))[3] = ((uint32_t) val) & 0xff; \
+        }
 
     #define READ_16_UNALIGNED(ptr) \
         ( (((uint8_t *)(ptr))[0] << 8) | ((uint8_t *)(ptr))[1] )
 
     #define WRITE_16_UNALIGNED(ptr, val) \
-        *((uint16_t *) (ptr)) = ( (((uint8_t *)(&val))[0] << 8) | ((uint8_t *)(&val))[1] )
+        { \
+            ((uint8_t *)(ptr))[0] = (((uint16_t) val) >> 8) & 0xff; \
+            ((uint8_t *)(ptr))[1] = ((uint16_t) val) & 0xff; \
+        }
 
     #define ENDIAN_SWAP_32(value) (value)
+
+#else
+    #error "Unsupported __BYTE_ORDER__ value."
 #endif
 
 #define UNUSED(x) (void) (x);