diff --git a/cpp2rust/converter/converter.cpp b/cpp2rust/converter/converter.cpp
index 99d7b036..a5c0a469 100644
--- a/cpp2rust/converter/converter.cpp
+++ b/cpp2rust/converter/converter.cpp
@@ -1816,6 +1816,20 @@ void Converter::ConvertFunctionToFunctionPointer(
   computed_expr_type_ = ComputedExprType::FreshPointer;
 }
 
+std::string Converter::ConvertFnPtrCallee(clang::Expr *arg) {
+  PushExprKind push(*this, ExprKind::Callee);
+  Buffer buf(*this);
+  Convert(arg);
+  return std::move(buf).str();
+}
+
+std::string Converter::ConvertFnPtrPlaceholder(clang::Expr *arg) {
+  auto proto =
+      arg->getType()->getPointeeType()->getAs<clang::FunctionProtoType>();
+  return std::format("({} as {} {})", ConvertFnPtrCallee(arg), keyword_unsafe_,
+                     ConvertFunctionPointerType(proto));
+}
+
 Converter::CallInfo Converter::CollectCallInfo(clang::CallExpr *expr) {
   using Kind = CallArg::Kind;
 
@@ -4607,22 +4621,20 @@ void Converter::PlaceholderCtx::dump() const {
                << ", declared_in_rule_as_rust_ptr: "
                << declared_in_rule_as_rust_ptr
                << ", access: " << static_cast<int>(access)
-               << ", param_type: " << param_type
+               << ", arg_idx: " << arg_idx
                << ", materialize_idx: " << materialize_idx << '\n';
 }
 
 std::string Converter::ConvertPlaceholder(clang::Expr *expr, clang::Expr *arg,
                                           const PlaceholderCtx &ph_ctx) {
   if (arg->getType()->isFunctionPointerType()) {
-    PushExprKind push(*this, ExprKind::Callee);
-    Buffer buf(*this);
-    Convert(arg);
-    return std::move(buf).str();
+    return ConvertFnPtrPlaceholder(arg);
   }
 
   if (ph_ctx.declared_in_rule_as_rust_ptr && arg->getType()->isArrayType()) {
-    return std::format("({} as {})", ConvertFreshPointer(arg),
-                       ph_ctx.param_type);
+    return std::format(
+        "({} as {})", ConvertFreshPointer(arg),
+        Mapper::GetParamType(GetCalleeOrExpr(expr), ph_ctx.arg_idx));
   }
 
   if (ph_ctx.needs_materialization()) {
@@ -4637,8 +4649,9 @@ std::string Converter::ConvertPlaceholder(clang::Expr *expr, clang::Expr *arg,
   }
 
   if (ph_ctx.needs_pointer_receiver()) {
-    return std::format("({} as {})", ConvertFreshObject(arg),
-                       ph_ctx.param_type);
+    return std::format(
+        "({} as {})", ConvertFreshObject(arg),
+        Mapper::GetParamType(GetCalleeOrExpr(expr), ph_ctx.arg_idx));
   }
 
   if (ph_ctx.needs_object_receiver()) {
@@ -4717,7 +4730,7 @@ std::string Converter::ConvertIRFragment(
       bool is_receiver = HasReceiver(expr) && arg_idx == 0;
 
       PlaceholderCtx ph_ctx{
-          .param_type = Mapper::GetParamType(GetCalleeOrExpr(expr), arg_idx),
+          .arg_idx = arg_idx,
           .implicit_convert_to = GetParamImplicitConvertTarget(expr, arg_idx),
           .materialize_ctx = ctx,
           .materialize_idx =
diff --git a/cpp2rust/converter/converter.h b/cpp2rust/converter/converter.h
index 6a4996cf..f2cb8c7b 100644
--- a/cpp2rust/converter/converter.h
+++ b/cpp2rust/converter/converter.h
@@ -221,7 +221,7 @@ class Converter : public clang::RecursiveASTVisitor<Converter> {
   };
 
   struct PlaceholderCtx {
-    std::string param_type;
+    unsigned arg_idx;
     std::optional<clang::QualType> implicit_convert_to;
     TempMaterializationCtx *materialize_ctx;
     int materialize_idx; // <0 = no idx, >=0 idx valid
@@ -309,6 +309,9 @@ class Converter : public clang::RecursiveASTVisitor<Converter> {
   virtual void
   ConvertFunctionToFunctionPointer(const clang::FunctionDecl *fn_decl);
 
+  std::string ConvertFnPtrCallee(clang::Expr *arg);
+  virtual std::string ConvertFnPtrPlaceholder(clang::Expr *arg);
+
   // Option<fn> implements Copy
   virtual bool FunctionPointerImplementsCopy() const { return true; }
 
diff --git a/cpp2rust/converter/mapper.cpp b/cpp2rust/converter/mapper.cpp
index 4def2784..b5ad34e4 100644
--- a/cpp2rust/converter/mapper.cpp
+++ b/cpp2rust/converter/mapper.cpp
@@ -682,10 +682,9 @@ std::string InstantiateTemplate(const clang::Expr *expr, unsigned n) {
   if (!rule) {
     return text;
   }
-  for (auto &ty : subs) {
-    if (ty) {
-      ty = mapTypeStringRecursive(*ty);
-    }
+  auto &ty = subs.at(n - 1);
+  if (ty) {
+    ty = mapTypeStringRecursive(*ty);
   }
   return instantiateTgt(subs, text);
 }
diff --git a/cpp2rust/converter/models/converter_refcount.cpp b/cpp2rust/converter/models/converter_refcount.cpp
index 8b6b7a19..625e62fc 100644
--- a/cpp2rust/converter/models/converter_refcount.cpp
+++ b/cpp2rust/converter/models/converter_refcount.cpp
@@ -1287,6 +1287,10 @@ void ConverterRefCount::ConvertFunctionToFunctionPointer(
   computed_expr_type_ = ComputedExprType::FreshPointer;
 }
 
+std::string ConverterRefCount::ConvertFnPtrPlaceholder(clang::Expr *arg) {
+  return ConvertFnPtrCallee(arg);
+}
+
 void ConverterRefCount::ConvertEqualsNullPtr(clang::Expr *expr) {
   StrCat('(');
   Convert(expr);
diff --git a/cpp2rust/converter/models/converter_refcount.h b/cpp2rust/converter/models/converter_refcount.h
index f588f6d1..790f7530 100644
--- a/cpp2rust/converter/models/converter_refcount.h
+++ b/cpp2rust/converter/models/converter_refcount.h
@@ -103,6 +103,8 @@ class ConverterRefCount final : public Converter {
   void
   ConvertFunctionToFunctionPointer(const clang::FunctionDecl *fn_decl) override;
 
+  std::string ConvertFnPtrPlaceholder(clang::Expr *arg) override;
+
   // FnPtr does not implement Copy
   bool FunctionPointerImplementsCopy() const override { return false; }
 
diff --git a/libcc2rs/src/callable.rs b/libcc2rs/src/callable.rs
new file mode 100644
index 00000000..f35dcfdc
--- /dev/null
+++ b/libcc2rs/src/callable.rs
@@ -0,0 +1,32 @@
+// Copyright (c) 2022-present INESC-ID.
+// Distributed under the MIT license that can be found in the LICENSE file.
+
+macro_rules! callable {
+    ($name:ident; $($a:ident: $A:ident),*) => {
+        pub trait $name<$($A,)* R> {
+            fn call(&self, $($a: $A),*) -> R;
+        }
+
+        impl<F, $($A,)* R> $name<$($A,)* R> for F
+        where
+            F: Fn($($A),*) -> R,
+        {
+            #[inline]
+            fn call(&self, $($a: $A),*) -> R {
+                self($($a),*)
+            }
+        }
+
+        impl<$($A,)* R> $name<$($A,)* R> for unsafe fn($($A),*) -> R {
+            #[inline]
+            fn call(&self, $($a: $A),*) -> R {
+                unsafe { self($($a),*) }
+            }
+        }
+    };
+}
+
+callable!(Callable0;);
+callable!(Callable1; a1: A1);
+callable!(Callable2; a1: A1, a2: A2);
+callable!(Callable3; a1: A1, a2: A2, a3: A3);
diff --git a/libcc2rs/src/lib.rs b/libcc2rs/src/lib.rs
index fb1f9be0..06b1e779 100644
--- a/libcc2rs/src/lib.rs
+++ b/libcc2rs/src/lib.rs
@@ -21,6 +21,9 @@ pub use libc_shims::*;
 mod fn_ptr;
 pub use fn_ptr::FnPtr;
 
+mod callable;
+pub use callable::*;
+
 mod inc;
 pub use inc::*;
 
diff --git a/rules/algorithm/src.cpp b/rules/algorithm/src.cpp
index 097b05cb..0d2946cd 100644
--- a/rules/algorithm/src.cpp
+++ b/rules/algorithm/src.cpp
@@ -9,6 +9,7 @@
 
 struct T2 {
   friend bool operator<(T2 a, T2 b) { return false; }
+  bool operator()(const T2 &, const T2 &) const;
 };
 
 struct T1 {
@@ -91,14 +92,7 @@ template <class T1, class T2> T1 f3(T1 first, T1 last, const T2 &value) {
   return std::find(first, last, value);
 }
 
-// TODO
-auto lambda = [](const T2 &a, const T2 &b) { return false; };
-void f6(T1 first, T1 last, decltype(lambda) comp) {
-  return std::stable_sort(first, last, comp);
-}
-
-template <typename T1, typename T2>
-void f7(T1 first, T1 last, bool (*comp)(const T2 &, const T2 &)) {
+void f6(T1 first, T1 last, T2 comp) {
   return std::stable_sort(first, last, comp);
 }
 
@@ -126,14 +120,7 @@ std::ostream_iterator<char> f13(std::string::iterator a0,
   return std::copy(a0, a1, a2);
 }
 
-// TODO
-auto lambda_nref = [](T2 a, T2 b) { return false; };
-void f14(T1 *first, T1 *last, decltype(lambda_nref) comp) {
-  return std::stable_sort(first, last, comp);
-}
-
-template <typename T1, typename T2>
-void f15(T1 *first, T1 *last, bool (*comp)(T2, T2)) {
+void f14(T1 *first, T1 *last, T2 comp) {
   return std::stable_sort(first, last, comp);
 }
 
diff --git a/rules/algorithm/tgt_refcount.rs b/rules/algorithm/tgt_refcount.rs
index 74866b39..66b8a801 100644
--- a/rules/algorithm/tgt_refcount.rs
+++ b/rules/algorithm/tgt_refcount.rs
@@ -38,16 +38,9 @@ fn f3<T1: PartialEq + Clone + ByteRepr>(a0: Ptr<T1>, a1: Ptr<T1>, a2: T1) -> Ptr
 
 fn f6<T1: Ord + Clone, T2>(a0: Ptr<T1>, a1: Ptr<T1>, a2: T2)
 where
-    T2: FnMut(Ptr<T1>, Ptr<T1>) -> bool,
+    T2: Callable2<Ptr<T1>, Ptr<T1>, bool>,
 {
-    a0.sort_with_cmp(a1.get_offset(), a2)
-}
-
-fn f7<T1: Ord + Clone, T2>(a0: Ptr<T1>, a1: Ptr<T1>, a2: T2)
-where
-    T2: FnMut(Ptr<T1>, Ptr<T1>) -> bool,
-{
-    a0.sort_with_cmp(a1.get_offset(), a2)
+    a0.sort_with_cmp(a1.get_offset(), |x, y| a2.call(x, y))
 }
 
 fn f8<T1: PartialOrd + Clone + ByteRepr>(a0: Ptr<T1>, a1: Ptr<T1>) -> Ptr<T1> {
@@ -109,17 +102,9 @@ fn f13(a0: Ptr<u8>, a1: Ptr<u8>, a2: &mut ::std::fs::File) -> ::std::fs::File {
 
 fn f14<T1: Ord + Clone + ByteRepr, T2>(a0: Ptr<T1>, a1: Ptr<T1>, a2: T2)
 where
-    T2: Fn(T1, T1) -> bool,
-{
-    let fun = |x: Ptr<T1>, y: Ptr<T1>| a2((x.read()).clone(), (y.read()).clone());
-    a0.sort_with_cmp(a1.get_offset(), fun)
-}
-
-fn f15<T1: Ord + Clone + ByteRepr, T2>(a0: Ptr<T1>, a1: Ptr<T1>, a2: T2)
-where
-    T2: Fn(T1, T1) -> bool,
+    T2: Callable2<T1, T1, bool>,
 {
-    let fun = |x: Ptr<T1>, y: Ptr<T1>| a2((x.read()).clone(), (y.read()).clone());
+    let fun = |x: Ptr<T1>, y: Ptr<T1>| a2.call((x.read()).clone(), (y.read()).clone());
     a0.sort_with_cmp(a1.get_offset(), fun)
 }
 
diff --git a/rules/algorithm/tgt_unsafe.rs b/rules/algorithm/tgt_unsafe.rs
index 101a2060..dbf6650e 100644
--- a/rules/algorithm/tgt_unsafe.rs
+++ b/rules/algorithm/tgt_unsafe.rs
@@ -1,6 +1,7 @@
 // Copyright (c) 2022-present INESC-ID.
 // Distributed under the MIT license that can be found in the LICENSE file.
 
+use libcc2rs::*;
 use std::io::{Seek, Write};
 
 unsafe fn f1<T1: Ord>(a0: *mut T1, a1: *mut T1) {
@@ -27,31 +28,15 @@ unsafe fn f3<T1: PartialEq>(a0: *mut T1, a1: *mut T1, a2: T1) -> *mut T1 {
     it
 }
 
-unsafe fn f6<T1: Ord, T2>(a0: *mut T1, a1: *mut T1, a2: &mut T2)
+unsafe fn f6<T1: Ord, T2>(a0: *mut T1, a1: *mut T1, a2: T2)
 where
-    T2: FnMut(&T1, &T1) -> bool,
+    T2: Callable2<*const T1, *const T1, bool>,
 {
     let len = a1.offset_from(a0) as usize;
     ::std::slice::from_raw_parts_mut(a0, len).sort_by(|x, y| {
-        if (a2)(x, y) {
+        if a2.call(x as *const _, y as *const _) {
             std::cmp::Ordering::Less
-        } else if (a2)(y, x) {
-            std::cmp::Ordering::Greater
-        } else {
-            std::cmp::Ordering::Equal
-        }
-    })
-}
-
-unsafe fn f7<T1: Ord, T2>(a0: *mut T1, a1: *mut T1, a2: &mut T2)
-where
-    T2: FnMut(&T1, &T1) -> bool,
-{
-    let len = a1.offset_from(a0) as usize;
-    ::std::slice::from_raw_parts_mut(a0, len).sort_by(|x, y| {
-        if (a2)(x, y) {
-            std::cmp::Ordering::Less
-        } else if (a2)(y, x) {
+        } else if a2.call(y as *const _, x as *const _) {
             std::cmp::Ordering::Greater
         } else {
             std::cmp::Ordering::Equal
@@ -113,31 +98,15 @@ unsafe fn f13(
     a2.try_clone().unwrap()
 }
 
-unsafe fn f14<T1: Ord + Copy, T2>(a0: *mut T1, a1: *mut T1, a2: &mut T2)
-where
-    T2: FnMut(T1, T1) -> bool,
-{
-    let len = a1.offset_from(a0) as usize;
-    ::std::slice::from_raw_parts_mut(a0, len).sort_by(|x, y| {
-        if (a2)(*x, *y) {
-            std::cmp::Ordering::Less
-        } else if (a2)(*y, *x) {
-            std::cmp::Ordering::Greater
-        } else {
-            std::cmp::Ordering::Equal
-        }
-    })
-}
-
-unsafe fn f15<T1: Ord + Copy, T2>(a0: *mut T1, a1: *mut T1, a2: &mut T2)
+unsafe fn f14<T1: Ord + Copy, T2>(a0: *mut T1, a1: *mut T1, a2: T2)
 where
-    T2: FnMut(T1, T1) -> bool,
+    T2: Callable2<T1, T1, bool>,
 {
     let len = a1.offset_from(a0) as usize;
     ::std::slice::from_raw_parts_mut(a0, len).sort_by(|x, y| {
-        if (a2)(*x, *y) {
+        if a2.call(*x, *y) {
             std::cmp::Ordering::Less
-        } else if (a2)(*y, *x) {
+        } else if a2.call(*y, *x) {
             std::cmp::Ordering::Greater
         } else {
             std::cmp::Ordering::Equal
diff --git a/tests/unit/out/refcount/fn_ptr_stable_sort.rs b/tests/unit/out/refcount/fn_ptr_stable_sort.rs
index be45ffe6..6ca928be 100644
--- a/tests/unit/out/refcount/fn_ptr_stable_sort.rs
+++ b/tests/unit/out/refcount/fn_ptr_stable_sort.rs
@@ -61,7 +61,7 @@ fn main_0() -> i32 {
     });
     (v.as_pointer() as Ptr<Item>).sort_with_cmp(
         (v.as_pointer() as Ptr<Item>).to_end().get_offset(),
-        Compare_0,
+        |x, y| Compare_0.call(x, y),
     );
     assert!(
         ((*(*(v.as_pointer() as Ptr<Item>)
diff --git a/tests/unit/out/refcount/stable_sort.rs b/tests/unit/out/refcount/stable_sort.rs
index 5da4a391..784fbf00 100644
--- a/tests/unit/out/refcount/stable_sort.rs
+++ b/tests/unit/out/refcount/stable_sort.rs
@@ -17,7 +17,8 @@ fn main_0() -> i32 {
                 let x: Value<i32> = Rc::new(RefCell::new(x));
                 let y: Value<i32> = Rc::new(RefCell::new(y));
                 return ((*x.borrow()) < (*y.borrow()));
-            })((x.read()).clone(), (y.read()).clone())
+            })
+            .call((x.read()).clone(), (y.read()).clone())
         };
         (arr1.as_pointer() as Ptr<i32>).sort_with_cmp(
             (arr1.as_pointer() as Ptr<i32>)
diff --git a/tests/unit/out/unsafe/fn_ptr_stable_sort.rs b/tests/unit/out/unsafe/fn_ptr_stable_sort.rs
index a0fd886a..2165c81e 100644
--- a/tests/unit/out/unsafe/fn_ptr_stable_sort.rs
+++ b/tests/unit/out/unsafe/fn_ptr_stable_sort.rs
@@ -28,9 +28,13 @@ unsafe fn main_0() -> i32 {
     {
         let len = v.as_mut_ptr().add(v.len()).offset_from(v.as_mut_ptr()) as usize;
         ::std::slice::from_raw_parts_mut(v.as_mut_ptr(), len).sort_by(|x, y| {
-            if (Compare_0)(x, y) {
+            if (Compare_0 as unsafe fn(*const Item, *const Item) -> bool)
+                .call(x as *const _, y as *const _)
+            {
                 std::cmp::Ordering::Less
-            } else if (Compare_0)(y, x) {
+            } else if (Compare_0 as unsafe fn(*const Item, *const Item) -> bool)
+                .call(y as *const _, x as *const _)
+            {
                 std::cmp::Ordering::Greater
             } else {
                 std::cmp::Ordering::Equal
diff --git a/tests/unit/out/unsafe/qsort_bsearch.rs b/tests/unit/out/unsafe/qsort_bsearch.rs
index 2a1ff8a6..c3fa5eb6 100644
--- a/tests/unit/out/unsafe/qsort_bsearch.rs
+++ b/tests/unit/out/unsafe/qsort_bsearch.rs
@@ -25,7 +25,10 @@ unsafe fn main_0() -> i32 {
         Some(std::mem::transmute::<
             *const (),
             unsafe extern "C" fn(*const ::libc::c_void, *const ::libc::c_void) -> i32,
-        >(cmp_int_0 as *const ())),
+        >(
+            (cmp_int_0 as unsafe fn(*const ::libc::c_void, *const ::libc::c_void) -> i32)
+                as *const (),
+        )),
     );
     let mut i: i32 = 0;
     'loop_: while ((((i) < (7)) as i32) != 0) {
@@ -41,7 +44,10 @@ unsafe fn main_0() -> i32 {
         Some(std::mem::transmute::<
             *const (),
             unsafe extern "C" fn(*const ::libc::c_void, *const ::libc::c_void) -> i32,
-        >(cmp_int_0 as *const ())),
+        >(
+            (cmp_int_0 as unsafe fn(*const ::libc::c_void, *const ::libc::c_void) -> i32)
+                as *const (),
+        )),
     ) as *mut i32);
     assert!((((!((hit).is_null())) as i32) != 0));
     assert!(((((*hit) == (7)) as i32) != 0));
@@ -54,7 +60,10 @@ unsafe fn main_0() -> i32 {
         Some(std::mem::transmute::<
             *const (),
             unsafe extern "C" fn(*const ::libc::c_void, *const ::libc::c_void) -> i32,
-        >(cmp_int_0 as *const ())),
+        >(
+            (cmp_int_0 as unsafe fn(*const ::libc::c_void, *const ::libc::c_void) -> i32)
+                as *const (),
+        )),
     ) as *mut i32);
     assert!(((((miss).is_null()) as i32) != 0));
     return 0;
diff --git a/tests/unit/out/unsafe/stable_sort.rs b/tests/unit/out/unsafe/stable_sort.rs
index 7427395a..da3cd9de 100644
--- a/tests/unit/out/unsafe/stable_sort.rs
+++ b/tests/unit/out/unsafe/stable_sort.rs
@@ -21,12 +21,14 @@ unsafe fn main_0() -> i32 {
         ::std::slice::from_raw_parts_mut(arr1.as_mut_ptr(), len).sort_by(|x, y| {
             if (|x: i32, y: i32| {
                 return ((x) < (y));
-            })(*x, *y)
+            })
+            .call(*x, *y)
             {
                 std::cmp::Ordering::Less
             } else if (|x: i32, y: i32| {
                 return ((x) < (y));
-            })(*y, *x)
+            })
+            .call(*y, *x)
             {
                 std::cmp::Ordering::Greater
             } else {