diff --git a/crates/concrete_check/src/lib.rs b/crates/concrete_check/src/lib.rs
index c10dc8b..2ef11a9 100644
--- a/crates/concrete_check/src/lib.rs
+++ b/crates/concrete_check/src/lib.rs
@@ -17,7 +17,7 @@ pub fn lowering_error_to_report(
             program_id,
         } => {
             let offset = span.from;
-            let path = file_paths[program_id].to_str().unwrap().to_string();
+            let path = file_paths[program_id].display().to_string();
             Report::build(ReportKind::Error, path.clone(), offset)
                 .with_code("ModuleNotFound")
                 .with_label(
@@ -33,7 +33,7 @@ pub fn lowering_error_to_report(
             function,
             program_id,
         } => {
-            let path = file_paths[program_id].to_str().unwrap().to_string();
+            let path = file_paths[program_id].display().to_string();
             Report::build(ReportKind::Error, path.clone(), span.from)
                 .with_code("FunctionNotFound")
                 .with_label(
@@ -48,7 +48,7 @@ pub fn lowering_error_to_report(
             name,
             program_id,
         } => {
-            let path = file_paths[program_id].to_str().unwrap().to_string();
+            let path = file_paths[program_id].display().to_string();
             Report::build(ReportKind::Error, path.clone(), span.from)
                 .with_code("StructFieldNotFound")
                 .with_label(
@@ -64,7 +64,7 @@ pub fn lowering_error_to_report(
             symbol,
             program_id,
         } => {
-            let path = file_paths[program_id].to_str().unwrap().to_string();
+            let path = file_paths[program_id].display().to_string();
             let offset = symbol.span.from;
             Report::build(ReportKind::Error, path.clone(), offset)
                 .with_code("ImportNotFound")
@@ -90,7 +90,7 @@ pub fn lowering_error_to_report(
             type_span,
             program_id,
         } => {
-            let path = file_paths[program_id].to_str().unwrap().to_string();
+            let path = file_paths[program_id].display().to_string();
             let mut labels = vec![Label::new((path.clone(), span.into()))
                 .with_message(format!(
                     "Can't mutate {name:?} because it's behind a immutable borrow"
@@ -115,7 +115,7 @@ pub fn lowering_error_to_report(
             name,
             program_id,
         } => {
-            let path = file_paths[program_id].to_str().unwrap().to_string();
+            let path = file_paths[program_id].display().to_string();
             Report::build(ReportKind::Error, path.clone(), span.from)
                 .with_code("UnrecognizedType")
                 .with_label(
@@ -131,7 +131,7 @@ pub fn lowering_error_to_report(
             id,
             program_id,
         } => {
-            let path = file_paths[program_id].to_str().unwrap().to_string();
+            let path = file_paths[program_id].display().to_string();
             Report::build(ReportKind::Error, path.clone(), span.from)
                 .with_code("E_ID")
                 .with_label(
@@ -147,7 +147,7 @@ pub fn lowering_error_to_report(
             message,
             program_id,
         } => {
-            let path = file_paths[program_id].to_str().unwrap().to_string();
+            let path = file_paths[program_id].display().to_string();
             Report::build(ReportKind::Error, path.clone(), span.from)
                 .with_code("NotYetImplemented")
                 .with_label(
@@ -163,7 +163,7 @@ pub fn lowering_error_to_report(
             expected,
             program_id,
         } => {
-            let path = file_paths[program_id].to_str().unwrap().to_string();
+            let path = file_paths[program_id].display().to_string();
             let mut labels = vec![Label::new((path.clone(), span.into()))
                 .with_message(format!(
                     "Unexpected type '{}', expected '{}'",
@@ -190,7 +190,7 @@ pub fn lowering_error_to_report(
             name,
             program_id,
         } => {
-            let path = file_paths[program_id].to_str().unwrap().to_string();
+            let path = file_paths[program_id].display().to_string();
             Report::build(ReportKind::Error, path.clone(), span.from)
                 .with_code("UseOfUndeclaredVariable")
                 .with_label(
@@ -205,7 +205,7 @@ pub fn lowering_error_to_report(
             name,
             program_id,
         } => {
-            let path = file_paths[program_id].to_str().unwrap().to_string();
+            let path = file_paths[program_id].display().to_string();
             Report::build(ReportKind::Error, path.clone(), span.from)
                 .with_code("ExternFnWithBody")
                 .with_label(
@@ -216,12 +216,32 @@ pub fn lowering_error_to_report(
                 .finish()
         }
         LoweringError::InternalError(msg, program_id) => {
-            let path = file_paths[program_id].to_str().unwrap().to_string();
+            let path = file_paths[program_id].display().to_string();
             Report::build(ReportKind::Error, path.clone(), 0)
                 .with_code("InternalError")
                 .with_message(msg)
                 .finish()
         }
+        LoweringError::CallParamCountMismatch {
+            span,
+            found,
+            needs,
+            program_id,
+        } => {
+            let path = file_paths[program_id].display().to_string();
+            Report::build(ReportKind::Error, path.clone(), span.from)
+                .with_code("CallParamCountMismatch")
+                .with_label(
+                    Label::new((path, span.into()))
+                        .with_message(format!(
+                            "function call parameter count mismatch: found {}, needs {}.",
+                            found, needs
+                        ))
+                        .with_color(colors.next()),
+                )
+                .finish()
+        }
+
         LoweringError::NotMutable {
             span,
             declare_span,
diff --git a/crates/concrete_driver/tests/checks.rs b/crates/concrete_driver/tests/checks.rs
index 6673a6e..41a9b4a 100644
--- a/crates/concrete_driver/tests/checks.rs
+++ b/crates/concrete_driver/tests/checks.rs
@@ -103,6 +103,39 @@ fn undeclared_var() {
     );
 }
 
+#[test]
+fn call_param_count_mismatch() {
+    let (source, name) = (
+        include_str!("invalid_programs/call_param_count_mismatch.con"),
+        "call_param_count_mismatch",
+    );
+    let error = check_invalid_program(source, name);
+
+    assert!(
+        matches!(
+            &error,
+            LoweringError::CallParamCountMismatch { found, needs, .. } if *found == 2 && *needs == 1
+        ),
+        "{:#?}",
+        error
+    );
+}
+
+#[test]
+fn call_param_type_mismatch() {
+    let (source, name) = (
+        include_str!("invalid_programs/call_param_type_mismatch.con"),
+        "call_param_type_mismatch",
+    );
+    let error = check_invalid_program(source, name);
+
+    assert!(
+        matches!(&error, LoweringError::UnexpectedType { .. }),
+        "{:#?}",
+        error
+    );
+}
+
 #[test]
 fn invalid_assign() {
     let (source, name) = (
diff --git a/crates/concrete_driver/tests/invalid_programs/call_param_count_mismatch.con b/crates/concrete_driver/tests/invalid_programs/call_param_count_mismatch.con
new file mode 100644
index 0000000..8fd3b1f
--- /dev/null
+++ b/crates/concrete_driver/tests/invalid_programs/call_param_count_mismatch.con
@@ -0,0 +1,9 @@
+mod Test {
+    fn main() -> i32 {
+        return hello(1, 2);
+    }
+
+    fn hello(a: i32) -> i32 {
+        return a * 2;
+    }
+}
diff --git a/crates/concrete_driver/tests/invalid_programs/call_param_type_mismatch.con b/crates/concrete_driver/tests/invalid_programs/call_param_type_mismatch.con
new file mode 100644
index 0000000..6ae9715
--- /dev/null
+++ b/crates/concrete_driver/tests/invalid_programs/call_param_type_mismatch.con
@@ -0,0 +1,10 @@
+mod Test {
+    fn main() -> i32 {
+        let x: u32 = 1;
+        return hello(x);
+    }
+
+    fn hello(a: i32) -> i32 {
+        return a * 2;
+    }
+}
diff --git a/crates/concrete_ir/src/lowering.rs b/crates/concrete_ir/src/lowering.rs
index beedda1..20a989f 100644
--- a/crates/concrete_ir/src/lowering.rs
+++ b/crates/concrete_ir/src/lowering.rs
@@ -1223,11 +1223,30 @@ fn lower_fn_call(
         }
     };
 
+    if args_ty.len() != info.args.len() {
+        return Err(LoweringError::CallParamCountMismatch {
+            span: info.span,
+            found: info.args.len(),
+            needs: args_ty.len(),
+            program_id: builder.get_module_body().id.program_id,
+        });
+    }
+
     let mut args = Vec::new();
 
     for (arg, arg_ty) in info.args.iter().zip(args_ty) {
-        let rvalue = lower_expression(builder, arg, Some(arg_ty.clone()))?;
-        args.push(rvalue.0);
+        let (rvalue, rvalue_ty, arg_span) = lower_expression(builder, arg, Some(arg_ty.clone()))?;
+
+        if rvalue_ty.kind != arg_ty.kind {
+            return Err(LoweringError::UnexpectedType {
+                span: arg_span,
+                found: rvalue_ty,
+                expected: arg_ty,
+                program_id: builder.get_module_body().id.program_id,
+            });
+        }
+
+        args.push(rvalue);
     }
 
     let dest_local = builder.add_local(Local::temp(ret_ty.clone()));
diff --git a/crates/concrete_ir/src/lowering/errors.rs b/crates/concrete_ir/src/lowering/errors.rs
index 8d329c8..94b9c67 100644
--- a/crates/concrete_ir/src/lowering/errors.rs
+++ b/crates/concrete_ir/src/lowering/errors.rs
@@ -88,4 +88,11 @@ pub enum LoweringError {
     },
     #[error("internal error: {0}")]
     InternalError(String, usize),
+    #[error("function call parameter count mismatch, found {found}, needs {needs}")]
+    CallParamCountMismatch {
+        span: Span,
+        found: usize,
+        needs: usize,
+        program_id: usize,
+    },
 }