diff --git a/src/corelib/tools/qdatetime.cpp b/src/corelib/tools/qdatetime.cpp
index 4f7d99b1d8..280f9ea006 100644
--- a/src/corelib/tools/qdatetime.cpp
+++ b/src/corelib/tools/qdatetime.cpp
@@ -100,24 +100,20 @@ static inline QDate fixedDate(int y, int m, int d)
 }
 
 /*
-  Until C++11, rounding direction is implementation-defined.
+  Division, rounding down (rather than towards zero).
 
-  For negative operands, implementations may chose to round down instead of
-  towards zero (truncation).  We only actually care about the case a < 0, as all
-  uses of floordiv have b > 0.  In this case, if rounding is down we have a % b
-  >= 0 and simple division works fine; but a % b = a - (a / b) * b always, so
-  rounding towards zero gives a % b <= 0; when < 0, we need to adjust.
-
-  Once we assume C++11, we can safely test a < 0 instead of a % b < 0.
+  From C++11 onwards, integer division is defined to round towards zero, so we
+  can rely on that when implementing this.  This is only used with denominator b
+  > 0, so we only have to treat negative numerator, a, specially.
  */
 static inline qint64 floordiv(qint64 a, int b)
 {
-    return (a - (a % b < 0 ? b - 1 : 0)) / b;
+    return (a - (a < 0 ? b - 1 : 0)) / b;
 }
 
 static inline int floordiv(int a, int b)
 {
-    return (a - (a % b < 0 ? b - 1 : 0)) / b;
+    return (a - (a < 0 ? b - 1 : 0)) / b;
 }
 
 static inline qint64 julianDayFromDate(int year, int month, int day)