diff --git a/tools/llvm-mc/Disassembler.cpp b/tools/llvm-mc/Disassembler.cpp
index e5c31ca..c29d82a 100644
--- a/tools/llvm-mc/Disassembler.cpp
+++ b/tools/llvm-mc/Disassembler.cpp
@@ -44,7 +44,7 @@
   uint64_t getExtent() const { return Bytes.size(); }
 
   int readByte(uint64_t Addr, uint8_t *Byte) const {
-    if (Addr > getExtent())
+    if (Addr >= getExtent())
       return -1;
     *Byte = Bytes[Addr].first;
     return 0;