diff --git a/compiler/mono/src/expr.rs b/compiler/mono/src/expr.rs
index 38cc5f2de9..f214420019 100644
--- a/compiler/mono/src/expr.rs
+++ b/compiler/mono/src/expr.rs
@@ -131,7 +131,12 @@ impl<'a> Expr<'a> {
     }
 }
 
-fn from_can_num<'a>(subs: &Subs, var: Variable, num: i64) -> Expr<'a> {
+enum IntOrFloat {
+    IntType,
+    FloatType,
+}
+
+fn to_int_or_float<'a>(subs: &Subs, var: Variable) -> IntOrFloat {
     // TODO FIXME Investigate why both INT_INT and INT_INTEGER (and same with
     // FLOAT_FLOAT and FLOAT_FLOATINGPOINT) are necessary here. It should
     // be one or the other, but not both! The fact that both are necessary
@@ -141,16 +146,16 @@ fn from_can_num<'a>(subs: &Subs, var: Variable, num: i64) -> Expr<'a> {
     match subs.get_without_compacting(var).content {
         Content::Alias(Symbol::INT_INT, args, _) | Content::Alias(Symbol::INT_INTEGER, args, _) => {
             debug_assert!(args.len() == 0);
-            Expr::Int(num)
+            IntOrFloat::IntType
         }
         Content::FlexVar(_) => {
             // If this was still a (Num *), assume compiling it to an Int
-            Expr::Int(num)
+            IntOrFloat::IntType
         }
         Content::Alias(Symbol::FLOAT_FLOAT, args, _)
         | Content::Alias(Symbol::FLOAT_FLOATINGPOINT, args, _) => {
             debug_assert!(args.len() == 0);
-            Expr::Float(num as f64)
+            IntOrFloat::FloatType
         }
         Content::Alias(Symbol::NUM_NUM, args, _) => {
             debug_assert!(args.len() == 1);
@@ -158,21 +163,21 @@ fn from_can_num<'a>(subs: &Subs, var: Variable, num: i64) -> Expr<'a> {
             match subs.get_without_compacting(args[0].1).content {
                 Content::Alias(Symbol::INT_INTEGER, args, _) => {
                     debug_assert!(args.len() == 0);
-                    Expr::Int(num)
+                    IntOrFloat::IntType
                 }
                 Content::FlexVar(_) => {
                     // If this was still a (Num *), assume compiling it to an Int
-                    Expr::Int(num)
+                    IntOrFloat::IntType
                 }
                 Content::Alias(Symbol::FLOAT_FLOATINGPOINT, args, _) => {
                     debug_assert!(args.len() == 0);
-                    Expr::Float(num as f64)
+                    IntOrFloat::FloatType
                 }
                 Content::Structure(FlatType::Apply(Symbol::ATTR_ATTR, attr_args)) => {
                     debug_assert!(attr_args.len() == 2);
 
                     // Recurse on the second argument
-                    from_can_num(subs, attr_args[1], num)
+                    to_int_or_float(subs, attr_args[1])
                 }
                 other => panic!(
                     "Unrecognized Num.Num alias type argument Content: {:?}",
@@ -184,7 +189,7 @@ fn from_can_num<'a>(subs: &Subs, var: Variable, num: i64) -> Expr<'a> {
             debug_assert!(attr_args.len() == 2);
 
             // Recurse on the second argument
-            from_can_num(subs, attr_args[1], num)
+            to_int_or_float(subs, attr_args[1])
         }
         other => panic!("Unrecognized Num type argument Content: {:?}", other),
     }
@@ -200,7 +205,10 @@ fn from_can<'a>(
     use roc_can::pattern::Pattern::*;
 
     match can_expr {
-        Num(var, num) => from_can_num(env.subs, var, num),
+        Num(var, num) => match to_int_or_float(env.subs, var) {
+            IntOrFloat::IntType => Expr::Int(num),
+            IntOrFloat::FloatType => Expr::Float(num as f64),
+        },
         Int(_, num) => Expr::Int(num),
         Float(_, num) => Expr::Float(num),
         Str(string) | BlockStr(string) => Expr::Str(env.arena.alloc(string)),
@@ -564,6 +572,30 @@ fn from_can_when<'a>(
             let (loc_when_pat2, loc_else) = iter.next().unwrap();
 
             match (&loc_when_pat1.value, &loc_when_pat2.value) {
+                (NumLiteral(var, num), NumLiteral(_, _)) | (NumLiteral(var, num), Underscore) => {
+                    let cond_lhs = arena.alloc(from_can(env, loc_cond.value, procs, None));
+                    let (builtin, cond_rhs_expr) = match to_int_or_float(env.subs, *var) {
+                        IntOrFloat::IntType => (Builtin::Int64, Expr::Int(*num)),
+                        IntOrFloat::FloatType => (Builtin::Float64, Expr::Float(*num as f64)),
+                    };
+
+                    let cond_rhs = arena.alloc(cond_rhs_expr);
+                    let pass = arena.alloc(from_can(env, loc_then.value, procs, None));
+                    let fail = arena.alloc(from_can(env, loc_else.value, procs, None));
+                    let ret_layout =
+                        Layout::from_var(arena, expr_var, env.subs).unwrap_or_else(|err| {
+                            panic!("TODO turn this into a RuntimeError {:?}", err)
+                        });
+
+                    Expr::Cond {
+                        cond_layout: Layout::Builtin(builtin),
+                        cond_lhs,
+                        cond_rhs,
+                        pass,
+                        fail,
+                        ret_layout,
+                    }
+                }
                 (IntLiteral(int), IntLiteral(_)) | (IntLiteral(int), Underscore) => {
                     let cond_lhs = arena.alloc(from_can(env, loc_cond.value, procs, None));
                     let cond_rhs = arena.alloc(Expr::Int(*int));