diff --git a/owlps-positioner/src/posutil.hh b/owlps-positioner/src/posutil.hh
index 7c7999e..c2cecfa 100644
--- a/owlps-positioner/src/posutil.hh
+++ b/owlps-positioner/src/posutil.hh
@@ -133,10 +133,12 @@ inline void PosUtil::to_upper(std::string &str)
 # define assert_uppercase(STR)
 #else // NDEBUG
 # define assert_uppercase(STR)                  \
-  ({std::string str_up((STR)) ;                 \
+  do {                                          \
+    std::string str((STR)) ;                    \
+    std::string str_up(str) ;                   \
     PosUtil::to_upper(str_up) ;                 \
-    assert(str_up == (STR)) ;                   \
-  })
+    assert(str_up == str) ;                     \
+  } while (0)
 #endif // NDEBUG