diff --git a/src/util/fixed_bit_vector.cpp b/src/util/fixed_bit_vector.cpp
index 78196f568..8843db736 100644
--- a/src/util/fixed_bit_vector.cpp
+++ b/src/util/fixed_bit_vector.cpp
@@ -26,7 +26,7 @@ Revision History:
 
 void fixed_bit_vector::set(fixed_bit_vector const& other, unsigned hi, unsigned lo) {
     if ((lo % 32) == 0) {
-        unsigned sz32 = (hi+1)/32;
+        unsigned sz32 = (hi-lo+1)/32;
         unsigned lo32 = lo/32;
         for (unsigned i = 0; i < sz32; ++i) {
             m_data[lo32 + i] = other.m_data[i];