diff --git a/apps/openmw/mwmechanics/spellcasting.cpp b/apps/openmw/mwmechanics/spellcasting.cpp
index 7f5a7fac5..6ea3f5472 100644
--- a/apps/openmw/mwmechanics/spellcasting.cpp
+++ b/apps/openmw/mwmechanics/spellcasting.cpp
@@ -714,7 +714,7 @@ namespace MWMechanics
             effect.mDuration = 1;
         if (!(magicEffect->mData.mFlags & ESM::MagicEffect::NoMagnitude))
         {
-            if (!magicEffect->mData.mFlags & ESM::MagicEffect::NoDuration)
+            if (!(magicEffect->mData.mFlags & ESM::MagicEffect::NoDuration))
                 magnitude = int((0.05 * y) / (0.1 * magicEffect->mData.mBaseCost));
             else
                 magnitude = int(y / (0.1 * magicEffect->mData.mBaseCost));