diff --git a/x86/x86asm/avx.go b/x86/x86asm/avx.go
index 148f72b..82c3472 100644
--- a/x86/x86asm/avx.go
+++ b/x86/x86asm/avx.go
@@ -76,6 +76,9 @@ func decodeAVX(src []byte, pos int, vex Prefix, vexIndex int, inst Inst, mode in
 
 	_ = evex_z // TODO: use zeroing mask if needed for output
 
+	if pos >= len(src) {
+		return inst, errors.New("truncated")
+	}
 	opbyte := src[pos]
 	pos++
 
diff --git a/x86/x86asm/decode_test.go b/x86/x86asm/decode_test.go
index 4543cd2..e409a2f 100644
--- a/x86/x86asm/decode_test.go
+++ b/x86/x86asm/decode_test.go
@@ -75,6 +75,11 @@ func TestDecodeDoesNotCrash(t *testing.T) {
 		[]byte{},
 		[]byte{0xc5},
 		[]byte{0xc4},
+		// Streams ending exactly at the end of a VEX or EVEX prefix,
+		// leaving no opcode byte.
+		[]byte{0xc5, 0xfc},
+		[]byte{0xc4, 0xe2, 0x7d},
+		[]byte{0x62, 0xf1, 0x7c, 0x48},
 	}
 	for _, test := range cases {
 		_, err := Decode([]byte(test), 64) // the only goal is that this line does not panic