diff --git a/decode.c b/decode.c
index b5dcb6c..ab43cfd 100644
--- a/decode.c
+++ b/decode.c
@@ -238,39 +238,60 @@ fd_decode(const uint8_t* buffer, size_t len_sz, int mode_int, uintptr_t address,
     int rex_off = -1;
     instr->segment = FD_REG_NONE;
 
-    while (LIKELY(off < len))
-    {
-        uint8_t prefix = buffer[off];
-        switch (UNLIKELY(prefix))
+#if defined(ARCH_386)
+    if (mode == DECODE_32) {
+        while (LIKELY(off < len))
         {
-        default: goto prefix_end;
-        // From segment overrides, the last one wins.
-        case 0x26: instr->segment = FD_REG_ES; break;
-        case 0x2e: instr->segment = FD_REG_CS; break;
-        case 0x36: instr->segment = FD_REG_SS; break;
-        case 0x3e: instr->segment = FD_REG_DS; break;
-        case 0x64: instr->segment = FD_REG_FS; break;
-        case 0x65: instr->segment = FD_REG_GS; break;
-        case 0x66: prefix_66 = true; break;
-        case 0x67: prefix_67 = true; break;
-        case 0xf0: prefix_lock = true; break;
-        // From REP/REPE and REPNZ, the last one wins; and for mandatory
-        // prefixes they have a higher priority than 66h (handled below).
-        case 0xf3: prefix_rep = 2; break;
-        case 0xf2: prefix_rep = 3; break;
-#if defined(ARCH_X86_64)
-        case 0x40: case 0x41: case 0x42: case 0x43: case 0x44: case 0x45:
-        case 0x46: case 0x47: case 0x48: case 0x49: case 0x4a: case 0x4b:
-        case 0x4c: case 0x4d: case 0x4e: case 0x4f:
-            if (mode != DECODE_64)
-                goto prefix_end;
-            prefix_rex = prefix;
-            rex_off = off;
-            break;
-#endif
+            uint8_t prefix = buffer[off];
+            switch (UNLIKELY(prefix))
+            {
+            default: goto prefix_end;
+            // From segment overrides, the last one wins.
+            case 0x26: instr->segment = FD_REG_ES; break;
+            case 0x2e: instr->segment = FD_REG_CS; break;
+            case 0x36: instr->segment = FD_REG_SS; break;
+            case 0x3e: instr->segment = FD_REG_DS; break;
+            case 0x64: instr->segment = FD_REG_FS; break;
+            case 0x65: instr->segment = FD_REG_GS; break;
+            case 0x66: prefix_66 = true; break;
+            case 0x67: prefix_67 = true; break;
+            case 0xf0: prefix_lock = true; break;
+            case 0xf3: prefix_rep = 2; break;
+            case 0xf2: prefix_rep = 3; break;
+            }
+            off++;
         }
-        off++;
     }
+#endif
+#if defined(ARCH_X86_64)
+    if (mode == DECODE_64) {
+        while (LIKELY(off < len))
+        {
+            uint8_t prefix = buffer[off];
+            switch (UNLIKELY(prefix))
+            {
+            default: goto prefix_end;
+            // ES/CS/SS/DS overrides are ignored.
+            case 0x26: case 0x2e: case 0x36: case 0x3e: break;
+            // From segment overrides, the last one wins.
+            case 0x64: instr->segment = FD_REG_FS; break;
+            case 0x65: instr->segment = FD_REG_GS; break;
+            case 0x66: prefix_66 = true; break;
+            case 0x67: prefix_67 = true; break;
+            case 0xf0: prefix_lock = true; break;
+            case 0xf3: prefix_rep = 2; break;
+            case 0xf2: prefix_rep = 3; break;
+            case 0x40: case 0x41: case 0x42: case 0x43: case 0x44: case 0x45:
+            case 0x46: case 0x47: case 0x48: case 0x49: case 0x4a: case 0x4b:
+            case 0x4c: case 0x4d: case 0x4e: case 0x4f:
+                prefix_rex = prefix;
+                rex_off = off;
+                break;
+            }
+            off++;
+        }
+    }
+#endif
 
 prefix_end:
     // REX prefix is only considered if it is the last prefix.
diff --git a/tests/test_decode.c b/tests/test_decode.c
index 9804e82..fa5beaf 100644
--- a/tests/test_decode.c
+++ b/tests/test_decode.c
@@ -58,12 +58,18 @@ main(int argc, char** argv)
 
     TEST("\x90", "[NOP]");
     TEST("\x90", "[NOP]");
-    TEST("\x2e\x90", "[cs:NOP]");
-    TEST("\x2e\x2e\x90", "[cs:NOP]");
-    TEST("\x2e\x26\x90", "[es:NOP]");
-    TEST("\x26\x2e\x90", "[cs:NOP]");
-    TEST("\x26\x65\x90", "[gs:NOP]");
-    TEST("\x65\x26\x90", "[es:NOP]");
+    TEST32("\x2e\x90", "[cs:NOP]");
+    TEST64("\x2e\x90", "[NOP]");
+    TEST32("\x2e\x2e\x90", "[cs:NOP]");
+    TEST64("\x2e\x2e\x90", "[NOP]");
+    TEST32("\x2e\x26\x90", "[es:NOP]");
+    TEST64("\x2e\x26\x90", "[NOP]");
+    TEST32("\x26\x2e\x90", "[cs:NOP]");
+    TEST64("\x26\x2e\x90", "[NOP]");
+    TEST32("\x26\x65\x90", "[gs:NOP]");
+    TEST64("\x26\x65\x90", "[gs:NOP]");
+    TEST32("\x65\x26\x90", "[es:NOP]");
+    TEST64("\x65\x26\x90", "[gs:NOP]");
     TEST("\x0f\x10\xc1", "[SSE_MOVUPS reg16:r0 reg16:r1]");
     TEST("\x66\x0f\x10\xc1", "[SSE_MOVUPD reg16:r0 reg16:r1]");
     TEST("\xf2\x66\x0f\x10\xc1", "[SSE_MOVSD reg16:r0 reg8:r1]");
@@ -73,7 +79,7 @@ main(int argc, char** argv)
     TEST64("\x48\x90", "[NOP]");
     TEST64("\x49\x90", "[XCHG reg8:r8 reg8:r0]");
     TEST64("\x48\x91", "[XCHG reg8:r1 reg8:r0]");
-    TEST64("\x48\x26\x91", "[es:XCHG reg4:r1 reg4:r0]");
+    TEST64("\x48\x26\x91", "[XCHG reg4:r1 reg4:r0]");
     TEST64("\x66\x90", "[NOP]");
     TEST("\x0f\xc7\x0f", "[CMPXCHGD_4 mem0:r7]");
     TEST64("\x48\x0f\xc7\x0f", "[CMPXCHGD_8 mem0:r7]");
@@ -285,7 +291,7 @@ main(int argc, char** argv)
     TEST("\x66\xc5\xf2\x2a\xc0", "UD"); // VEX+66
     TEST("\xf0\xc5\xf2\x2a\xc0", "UD"); // VEX+LOCK
     TEST64("\x40\xc5\xf2\x2a\xc0", "UD"); // VEX+REX
-    TEST64("\x40\x26\xc5\xf2\x2a\xc0", "[es:VCVTSI2SS reg16:r0 reg16:r1 reg4:r0]"); // VEX+REX, but REX doesn't precede VEX
+    TEST64("\x40\x26\xc5\xf2\x2a\xc0", "[VCVTSI2SS reg16:r0 reg16:r1 reg4:r0]"); // VEX+REX, but REX doesn't precede VEX
 
     TEST("\xf3\x0f\x7e\x5c\x24\x08", "[SSE_MOVQ reg16:r3 mem8:r4+0x8]");
     TEST32("\xc4\xe1\x00\x58\xc1", "[VADDPS reg16:r0 reg16:r7 reg16:r1]"); // MSB in vvvv ignored