diff --git a/.gitignore b/.gitignore
index 647529b4f..7757275f3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -64,3 +64,4 @@ src/util/version.h
 src/api/java/Native.cpp
 src/api/java/Native.java
 src/api/java/enumerations/*.java
+*.bak
diff --git a/src/util/mpz.cpp b/src/util/mpz.cpp
index bd7f30a76..94df9f78d 100644
--- a/src/util/mpz.cpp
+++ b/src/util/mpz.cpp
@@ -1535,7 +1535,7 @@ bool mpz_manager<SYNCH>::is_power_of_two(mpz const & a, unsigned & shift) {
         return false;
     if (is_small(a)) {
         if (::is_power_of_two(a.m_val)) {
-            shift = ::log2(a.m_val);
+            shift = ::log2((unsigned)a.m_val);
             return true;
         }
         else {
@@ -1838,7 +1838,7 @@ unsigned mpz_manager<SYNCH>::log2(mpz const & a) {
     if (is_nonpos(a))
         return 0;
     if (is_small(a))
-        return ::log2(a.m_val);
+        return ::log2((unsigned)a.m_val);
 #ifndef _MP_GMP
     COMPILE_TIME_ASSERT(sizeof(digit_t) == 8 || sizeof(digit_t) == 4);
     mpz_cell * c     = a.m_ptr;
@@ -1860,7 +1860,7 @@ unsigned mpz_manager<SYNCH>::mlog2(mpz const & a) {
     if (is_nonneg(a))
         return 0;
     if (is_small(a))
-        return ::log2(-a.m_val);
+        return ::log2((unsigned)-a.m_val);
 #ifndef _MP_GMP
     COMPILE_TIME_ASSERT(sizeof(digit_t) == 8 || sizeof(digit_t) == 4);
     mpz_cell * c     = a.m_ptr;