diff --git a/libunwind/src/DwarfInstructions.hpp b/libunwind/src/DwarfInstructions.hpp
index 48ef1866d6e..ee98f538d43 100644
--- a/libunwind/src/DwarfInstructions.hpp
+++ b/libunwind/src/DwarfInstructions.hpp
@@ -433,7 +433,7 @@ DwarfInstructions<A, R>::evaluateExpression(pint_t expression, A &addressSpace,
       // pick from
       reg = addressSpace.get8(p);
       p += 1;
-      value = sp[-reg];
+      value = sp[-(int)reg];
       *(++sp) = value;
       if (log)
         fprintf(stderr, "duplicate %d in stack\n", reg);