diff --git a/apps/opencs/model/tools/regioncheck.cpp b/apps/opencs/model/tools/regioncheck.cpp
index 2fdff5f38..adb3dcd54 100644
--- a/apps/opencs/model/tools/regioncheck.cpp
+++ b/apps/opencs/model/tools/regioncheck.cpp
@@ -33,5 +33,12 @@ void CSMTools::RegionCheckStage::perform (int stage, CSMDoc::Messages& messages)
 
     /// \todo test that the ID in mSleeplist exists
 
+    // test that chances add up to 100
+    int chances = region.mData.mClear + region.mData.mCloudy + region.mData.mFoggy + region.mData.mOvercast +
+        region.mData.mRain + region.mData.mThunder + region.mData.mAsh + region.mData.mBlight +
+        region.mData.mA + region.mData.mB;
+    if (chances != 100)
+        messages.add(id, "Weather chances do not add up to 100", "", CSMDoc::Message::Severity_Error);
+
     /// \todo check data members that can't be edited in the table view
 }