diff --git a/opm/parser/eclipse/EclipseState/Schedule/UDQ/UDQConfig.hpp b/opm/parser/eclipse/EclipseState/Schedule/UDQ/UDQConfig.hpp
index 9e7a2c237..d38279f8b 100644
--- a/opm/parser/eclipse/EclipseState/Schedule/UDQ/UDQConfig.hpp
+++ b/opm/parser/eclipse/EclipseState/Schedule/UDQ/UDQConfig.hpp
@@ -65,6 +65,7 @@ namespace Opm {
 
         void eval(std::size_t report_step, const WellMatcher& wm, SummaryState& st, UDQState& udq_state) const;
         const UDQDefine& define(const std::string& key) const;
+        const UDQAssign& assign(const std::string& key) const;
         std::vector<UDQDefine> definitions() const;
         std::vector<UDQDefine> definitions(UDQVarType var_type) const;
         std::vector<UDQInput> input() const;
diff --git a/src/opm/parser/eclipse/EclipseState/Schedule/UDQ/UDQConfig.cpp b/src/opm/parser/eclipse/EclipseState/Schedule/UDQ/UDQConfig.cpp
index dd1eba5c5..5d31d001c 100644
--- a/src/opm/parser/eclipse/EclipseState/Schedule/UDQ/UDQConfig.cpp
+++ b/src/opm/parser/eclipse/EclipseState/Schedule/UDQ/UDQConfig.cpp
@@ -159,6 +159,10 @@ namespace Opm {
         }
     }
 
+    const UDQAssign& UDQConfig::assign(const std::string& key) const {
+        return this->m_assignments.at(key);
+    }
+
     const UDQDefine& UDQConfig::define(const std::string& key) const {
         return this->m_definitions.at(key);
     }
diff --git a/src/opm/parser/eclipse/EclipseState/Schedule/UDQ/UDQSet.cpp b/src/opm/parser/eclipse/EclipseState/Schedule/UDQ/UDQSet.cpp
index 9f03dba16..4574b539c 100644
--- a/src/opm/parser/eclipse/EclipseState/Schedule/UDQ/UDQSet.cpp
+++ b/src/opm/parser/eclipse/EclipseState/Schedule/UDQ/UDQSet.cpp
@@ -478,37 +478,59 @@ UDQScalar operator/(double lhs, const UDQScalar& rhs) {
 
 namespace {
 
+bool is_scalar(const UDQSet& udq_set) {
+    if (udq_set.var_type() == UDQVarType::SCALAR)
+        return true;
+
+    if (udq_set.var_type() == UDQVarType::FIELD_VAR)
+        return true;
+
+    return false;
+}
+
+
 /*
   If one result set is scalar and the other represents a set of wells/groups,
   the scalar result is promoted to a set of the right type.
-*/
-UDQSet udq_cast(const UDQSet& lhs, const UDQSet& rhs)
-{
-    if (lhs.size() != rhs.size()) {
-        if (lhs.var_type() != UDQVarType::SCALAR) {
-            auto msg = fmt::format("Type/size mismatch when combining UDQs {}(size={}, type={}) and {}(size={}, type={})",
-                                   lhs.name(), lhs.size(), lhs.var_type(),
-                                   rhs.name(), rhs.size(), rhs.var_type());
-            throw std::logic_error(msg);
-        }
 
+  This function is quite subconcious about FIELD / SCALAR.
+*/
+std::pair<UDQSet, UDQSet> udq_cast(const UDQSet& lhs, const UDQSet& rhs)
+{
+    if (lhs.var_type() == rhs.var_type())
+        return std::make_pair(lhs,rhs);
+
+    if (lhs.size() == rhs.size())
+        return std::make_pair(lhs,rhs);
+
+    if (is_scalar(lhs)) {
         if (rhs.var_type() == UDQVarType::WELL_VAR)
-            return UDQSet::wells(lhs.name(), rhs.wgnames(), lhs[0].get());
+            return std::make_pair(UDQSet::wells(lhs.name(), rhs.wgnames(), lhs[0].get()), rhs);
 
         if (rhs.var_type() == UDQVarType::GROUP_VAR)
-            return UDQSet::groups(lhs.name(), rhs.wgnames(), lhs[0].get());
+            return std::make_pair(UDQSet::groups(lhs.name(), rhs.wgnames(), lhs[0].get()), rhs);
+    }
 
-        throw std::logic_error("Don't have a clue");
-    } else
-        return lhs;
+    if (is_scalar(rhs)) {
+        if (lhs.var_type() == UDQVarType::WELL_VAR)
+            return std::make_pair(lhs, UDQSet::wells(rhs.name(), lhs.wgnames(), rhs[0].get()));
+
+        if (lhs.var_type() == UDQVarType::GROUP_VAR)
+            return std::make_pair(lhs, UDQSet::groups(rhs.name(), lhs.wgnames(), rhs[0].get()));
+    }
+
+    auto msg = fmt::format("Type/size mismatch when combining UDQs {}(size={}, type={}) and {}(size={}, type={})",
+                           lhs.name(), lhs.size(), lhs.var_type(),
+                           rhs.name(), rhs.size(), rhs.var_type());
+    throw std::logic_error(msg);
 }
 
 }
 
 UDQSet operator+(const UDQSet&lhs, const UDQSet& rhs) {
-    UDQSet sum = udq_cast(lhs, rhs);
-    sum += rhs;
-    return sum;
+    auto [left,right] = udq_cast(lhs, rhs);
+    left += right;
+    return left;
 }
 
 UDQSet operator+(const UDQSet&lhs, double rhs) {
@@ -524,9 +546,9 @@ UDQSet operator+(double lhs, const UDQSet& rhs) {
 }
 
 UDQSet operator-(const UDQSet&lhs, const UDQSet& rhs) {
-    UDQSet diff = udq_cast(lhs, rhs);
-    diff -= rhs;
-    return diff;
+    auto [left,right] = udq_cast(lhs, rhs);
+    left -= right;
+    return left;
 }
 
 UDQSet operator-(const UDQSet&lhs, double rhs) {
@@ -542,9 +564,9 @@ UDQSet operator-(double lhs, const UDQSet& rhs) {
 }
 
 UDQSet operator*(const UDQSet&lhs, const UDQSet& rhs) {
-    UDQSet prod = udq_cast(lhs, rhs);
-    prod *= rhs;
-    return prod;
+    auto [left,right] = udq_cast(lhs, rhs);
+    left *= right;
+    return left;
 }
 
 UDQSet operator*(const UDQSet&lhs, double rhs) {
@@ -560,9 +582,9 @@ UDQSet operator*(double lhs, const UDQSet& rhs) {
 }
 
 UDQSet operator/(const UDQSet&lhs, const UDQSet& rhs) {
-    UDQSet frac = udq_cast(lhs, rhs);
-    frac /= rhs;
-    return frac;
+    auto [left,right] = udq_cast(lhs, rhs);
+    left /= right;
+    return left;
 }
 
 UDQSet operator/(const UDQSet&lhs, double rhs) {
diff --git a/tests/parser/UDQTests.cpp b/tests/parser/UDQTests.cpp
index e0a419c60..f7b0cbc31 100644
--- a/tests/parser/UDQTests.cpp
+++ b/tests/parser/UDQTests.cpp
@@ -2484,3 +2484,48 @@ TSTEP
         BOOST_CHECK( !udq_state.define(def.keyword(), def.status()));
     }
 }
+
+BOOST_AUTO_TEST_CASE(UDQ_TYPE_CAST) {
+
+    std::string valid = R"(
+SCHEDULE
+
+UDQ
+   ASSIGN FUBHPP1 100 /
+/
+
+TSTEP
+10 /
+
+UDQ
+   DEFINE FU_TIME TIME /
+   DEFINE WUDELTA WBHP '*' - FUBHPP1 /
+   DEFINE WU_TEST WUBHPINI '*' - (WGPR '*')/2000.0 /
+
+/
+
+)";
+
+
+
+    auto schedule = make_schedule(valid);
+    UDQState udq_state(0);
+    SummaryState st(std::chrono::system_clock::now());
+    UDQFunctionTable udqft;
+    UDQContext context(udqft, WellMatcher({"W1", "W2", "W3"}), st, udq_state);
+    st.update_well_var("W1", "WBHP", 400);
+    st.update_well_var("W2", "WBHP", 300);
+    st.update_well_var("W3", "WBHP", 200);
+
+    const auto& udq = schedule.getUDQConfig(1);
+    {
+        const auto& ass = udq.assign("FUBHPP1");
+        context.update_assign(1, "FUBHPP1", ass.eval());
+    }
+    const auto& def = udq.define("WUDELTA");
+    auto res = def.eval(context);
+
+    BOOST_CHECK_EQUAL(res["W1"].get(), 300);
+    BOOST_CHECK_EQUAL(res["W2"].get(), 200);
+    BOOST_CHECK_EQUAL(res["W3"].get(), 100);
+}