diff --git a/Compiler/BackEnd/ExpressionSolve.mo b/Compiler/BackEnd/ExpressionSolve.mo
index ddfd7afab0b..6622fd8f7bd 100644
--- a/Compiler/BackEnd/ExpressionSolve.mo
+++ b/Compiler/BackEnd/ExpressionSolve.mo
@@ -556,6 +556,14 @@ algorithm
         lhs =  Expression.makeDiff(e2, lhs);
         (res,asserts) = solve(lhs,rhs,inExp3);
       then(res, asserts);
+    // -f(a) = b => f(a) = -b
+    case(DAE.UNARY(DAE.UMINUS(ty=tp), e1),_,DAE.CREF(componentRef = cr),_)  
+      equation
+        true = Expression.expHasCref(e1, cr);
+        false = Expression.expHasCref(inExp2, cr);
+        e2 = DAE.UNARY(DAE.UMINUS(tp),inExp2);
+        (res,asserts) = solve(e1,e2,inExp3);
+      then(res, asserts);
 
     // 0 = a*(b-c)  solve for b
     case (_,_,DAE.CREF(componentRef = _),_)