Index: ps/trunk/source/maths/FixedVector2D.h
===================================================================
--- ps/trunk/source/maths/FixedVector2D.h
+++ ps/trunk/source/maths/FixedVector2D.h
@@ -204,6 +204,7 @@
 
 	/**
 	 * Compute the dot product of this vector with another.
+	 * Likely to overflow if both vectors are large-ish (around the 200 range).
 	 */
 	fixed Dot(const CFixedVector2D& v) const
 	{
@@ -219,6 +220,16 @@
 		return ret;
 	}
 
+	/**
+	 * @return -1, 0 or 1 if this and @v face respectively opposite directions, perpendicular, or same directions.
+	 */
+	int RelativeOrientation(const CFixedVector2D& v) const
+	{
+		i64 x = MUL_I64_I32_I32(X.GetInternalValue(), v.X.GetInternalValue());
+		i64 y = MUL_I64_I32_I32(Y.GetInternalValue(), v.Y.GetInternalValue());
+		return x > -y ? 1 : x < -y ? -1 : 0;
+	}
+
 	CFixedVector2D Perpendicular() const
 	{
 		return CFixedVector2D(Y, -X);
Index: ps/trunk/source/simulation2/components/CCmpUnitMotion.cpp
===================================================================
--- ps/trunk/source/simulation2/components/CCmpUnitMotion.cpp
+++ ps/trunk/source/simulation2/components/CCmpUnitMotion.cpp
@@ -1149,7 +1149,7 @@
 
 			// Check if we anticipate the target to go through us, in which case we shouldn't anticipate
 			// (or e.g. units fleeing might suddenly turn around towards their attacker).
-			if ((out - cmpPosition->GetPosition2D()).Dot(tempPos - cmpPosition->GetPosition2D()) >= fixed::Zero())
+			if ((out - cmpPosition->GetPosition2D()).RelativeOrientation(tempPos - cmpPosition->GetPosition2D()) >= 0)
 				out = tempPos;
 		}
 	}
Index: ps/trunk/source/simulation2/helpers/Geometry.cpp
===================================================================
--- ps/trunk/source/simulation2/helpers/Geometry.cpp
+++ ps/trunk/source/simulation2/helpers/Geometry.cpp
@@ -342,13 +342,13 @@
 	fixed hh = halfSize.Y;
 
 	CFixedVector2D p = axis.Perpendicular();
-	if (p.Dot((u.Multiply(hw) + v.Multiply(hh)) - a) <= fixed::Zero())
+	if (p.RelativeOrientation(u.Multiply(hw) + v.Multiply(hh) - a) <= 0)
 		return true;
-	if (p.Dot((u.Multiply(hw) - v.Multiply(hh)) - a) <= fixed::Zero())
+	if (p.RelativeOrientation(u.Multiply(hw) - v.Multiply(hh) - a) <= 0)
 		return true;
-	if (p.Dot((-u.Multiply(hw) - v.Multiply(hh)) - a) <= fixed::Zero())
+	if (p.RelativeOrientation(-u.Multiply(hw) - v.Multiply(hh) - a) <= 0)
 		return true;
-	if (p.Dot((-u.Multiply(hw) + v.Multiply(hh)) - a) <= fixed::Zero())
+	if (p.RelativeOrientation(-u.Multiply(hw) + v.Multiply(hh) - a) <= 0)
 		return true;
 
 	return false;