diff --git a/poincare/src/multiplication.cpp b/poincare/src/multiplication.cpp
index 509e2696f..9eacf74ad 100644
--- a/poincare/src/multiplication.cpp
+++ b/poincare/src/multiplication.cpp
@@ -264,8 +264,15 @@ Expression Multiplication::removeUnit(Expression * unit) {
     if (!currentUnit.isUninitialized()) {
       unitMult.addChildAtIndexInPlace(currentUnit, resultChildrenCount, resultChildrenCount);
       resultChildrenCount++;
-      assert(childAtIndex(i).isRationalOne());
-      removeChildAtIndexInPlace(i--);
+      if (childAtIndex(i).isRationalOne()) {
+        removeChildAtIndexInPlace(i--);
+      } else {
+        /* If the child was a unit convert, it replaced itself with an undefined
+         * during the removeUnit. */
+        assert(childAtIndex(i).isUndefined());
+        *unit = Expression();
+        return replaceWithUndefinedInPlace();
+      }
     }
   }
   if (resultChildrenCount == 0) {
diff --git a/poincare/test/simplification.cpp b/poincare/test/simplification.cpp
index 13860225b..64175b73c 100644
--- a/poincare/test/simplification.cpp
+++ b/poincare/test/simplification.cpp
@@ -1317,6 +1317,17 @@ QUIZ_CASE(poincare_simplification_user_function_with_convert) {
         Symbol::Builder('x')));
   assert_expression_reduce(e);
   assert_parsed_expression_simplify_to("e^(f(0))", "undef");
+
+  e = Store::Builder(
+      UnitConvert::Builder(
+        Rational::Builder(0),
+        Unit::Second()),
+      Function::Builder(
+        "f", 1,
+        Symbol::Builder('x')));
+  assert_expression_reduce(e);
+  assert_parsed_expression_simplify_to("0f(0)", "undef");
+
   Ion::Storage::sharedStorage()->recordNamed("f.func").destroy();
 }