diff --git a/check/src/typecheck.rs b/check/src/typecheck.rs
index bf68ab88f7..585a89eb6a 100644
--- a/check/src/typecheck.rs
+++ b/check/src/typecheck.rs
@@ -3,7 +3,6 @@
 //! checking of types are done in the `unify_type` and `kindcheck` modules.
 use std::{
     borrow::{BorrowMut, Cow},
-    iter::once,
     mem,
     ops::Deref,
     sync::Arc,
@@ -1360,25 +1359,25 @@ impl<'a> Typecheck<'a> {
         let mut return_variables = FnvSet::default();
 
         for arg in &mut **implicit_args {
-            let arg_ty = self.subs.new_var();
-            let ret_ty = self.subs.new_var();
-            let f = self
-                .subs
-                .function_implicit(once(arg_ty.clone()), ret_ty.clone());
-
-            self.subsumes(arg.span, ErrorOrder::ExpectedActual, &f, func_type.clone());
+            let (arg_typ, ret_typ) = self.subsume_function(
+                arg.span.start(),
+                arg.span,
+                ArgType::Implicit,
+                func_type.clone(),
+                &mut Vec::new(),
+            );
 
-            let arg_ty = self.typecheck(arg, ModType::wobbly(&arg_ty));
+            let arg_typ = self.typecheck(arg, ModType::wobbly(&arg_typ));
 
-            if arg_ty.modifier == TypeModifier::Rigid {
-                types::walk_type(&self.subs.zonk(&arg_ty), &mut |typ: &RcType| {
+            if arg_typ.modifier == TypeModifier::Rigid {
+                types::walk_type(&self.subs.zonk(&arg_typ), &mut |typ: &RcType| {
                     if let Type::Variable(var) = &**typ {
                         return_variables.insert(var.id);
                     }
                 });
             }
 
-            func_type = ret_ty;
+            func_type = ret_typ;
         }
 
         let mut not_a_function_index = None;
@@ -1386,8 +1385,13 @@ impl<'a> Typecheck<'a> {
         let mut prev_arg_end = implicit_args.last().map_or(span, |arg| arg.span).end();
         for arg in args.map(|arg| arg.borrow_mut()) {
             let errors_before = self.errors.len();
-            let (arg_ty, ret_ty) =
-                self.subsume_function(prev_arg_end, arg.span, func_type.clone(), implicit_args);
+            let (arg_ty, ret_ty) = self.subsume_function(
+                prev_arg_end,
+                arg.span,
+                ArgType::Explicit,
+                func_type.clone(),
+                implicit_args,
+            );
 
             if errors_before != self.errors.len() {
                 self.errors.pop();
@@ -2754,35 +2758,6 @@ impl<'a> Typecheck<'a> {
         }
     }
 
-    fn subsume_function(
-        &mut self,
-        prev_arg_end: BytePos,
-        span: Span<BytePos>,
-        actual: RcType,
-        implicit_args: &mut Vec<SpannedExpr<Symbol>>,
-    ) -> (RcType, RcType) {
-        let actual = self.remove_aliases(actual);
-        match actual.as_function_with_type() {
-            Some((ArgType::Explicit, arg, ret)) => return (arg.clone(), ret.clone()),
-            _ => (),
-        }
-
-        let arg_ty = self.subs.new_var();
-        let ret_ty = self.subs.new_var();
-        let f = self.subs.function(once(arg_ty.clone()), ret_ty.clone());
-
-        self.subsumes_implicit(
-            span,
-            ErrorOrder::ExpectedActual,
-            &f,
-            actual,
-            &mut |implicit_arg| {
-                implicit_args.push(pos::spanned2(prev_arg_end, span.start(), implicit_arg));
-            },
-        );
-        (arg_ty, ret_ty)
-    }
-
     fn instantiate_sigma(
         &mut self,
         span: Span<BytePos>,
@@ -2811,17 +2786,57 @@ impl<'a> Typecheck<'a> {
         }
     }
 
+    fn subsume_function(
+        &mut self,
+        prev_arg_end: BytePos,
+        span: Span<BytePos>,
+        arg_type: ArgType,
+        actual: RcType,
+        implicit_args: &mut Vec<SpannedExpr<Symbol>>,
+    ) -> (RcType, RcType) {
+        let (_, a, r) = self.merge_function(Some(arg_type), actual, &mut |self_, f, actual| {
+            self_.subsumes_implicit(
+                span,
+                ErrorOrder::ExpectedActual,
+                &f,
+                actual,
+                &mut |implicit_arg| {
+                    implicit_args.push(pos::spanned2(prev_arg_end, span.start(), implicit_arg));
+                },
+            );
+        });
+        (a, r)
+    }
+
     fn unify_function(&mut self, span: Span<BytePos>, actual: RcType) -> (ArgType, RcType, RcType) {
+        self.merge_function(None, actual, &mut |self_, f, actual| {
+            self_.unify_span(span, &f, actual);
+        })
+    }
+
+    fn merge_function(
+        &mut self,
+        function_arg_type: Option<ArgType>,
+        actual: RcType,
+        merge_fn: &mut FnMut(&mut Self, &RcType, RcType),
+    ) -> (ArgType, RcType, RcType) {
         let actual = self.remove_aliases(actual);
         match actual.as_function_with_type() {
-            Some((arg_type, arg, ret)) => return (arg_type, arg.clone(), ret.clone()),
-            None => (),
+            Some((found_arg_type, arg, ret))
+                if function_arg_type == Some(found_arg_type) || function_arg_type == None =>
+            {
+                return (found_arg_type, arg.clone(), ret.clone())
+            }
+            _ => (),
         }
         let arg = self.subs.new_var();
         let ret = self.subs.new_var();
-        let f = self.subs.function(Some(arg.clone()), ret.clone());
-        self.unify_span(span, &f, actual);
-        (ArgType::Explicit, arg, ret)
+        let arg_type = function_arg_type.unwrap_or(ArgType::Explicit);
+        let f = self
+            .subs
+            .function_type(arg_type, Some(arg.clone()), ret.clone());
+        merge_fn(self, &f, actual);
+        (arg_type, arg, ret)
     }
 
     fn unify_span(&mut self, span: Span<BytePos>, expected: &RcType, actual: RcType) -> RcType {