diff --git a/crates/main/src/main.rs b/crates/main/src/main.rs
index 90e5044..75b98d7 100644
--- a/crates/main/src/main.rs
+++ b/crates/main/src/main.rs
@@ -63,14 +63,19 @@ fn main() {
 
                     // Typecheck the HIR
                     match check(&ir) {
-                        Ok(_) => {},
-                        Err(err) => {
-                            diagnostics.add_typecheck_error(err);
+                        Ok(_) => {
+                            logif!(0, format!("Typechecking took {}ms", start.elapsed().as_millis()));
+                        },
+                        Err(errs) => {
+                            for err in errs {
+                                diagnostics.add_typecheck_error(err);
+                            }
                             diagnostics.display(src);
-                            logif!(0, "Typechecking failed");
+                            logif!(2, "Typechecking failed");
                             std::process::exit(1);
                         }
                     }
+                    dbg!(check(&ir));
 
                     // Report lowering errors if any
                     if diagnostics.has_error() {
diff --git a/crates/typecheck/src/lib.rs b/crates/typecheck/src/lib.rs
index 592e26b..8105a5f 100644
--- a/crates/typecheck/src/lib.rs
+++ b/crates/typecheck/src/lib.rs
@@ -1,4 +1,4 @@
-use hir::{IR, IRKind};
+use hir::{IR, IRKind, Value};
 
 #[derive(Debug)]
 pub enum TypecheckErrorKind {
@@ -29,6 +29,95 @@ pub struct TypecheckError {
     pub span: std::ops::Range<usize>,
 }
 
-pub fn check(ir: &Vec<IR>) -> Result<(), TypecheckError> {
-    todo!();
+pub fn check(irs: &Vec<IR>) -> Result<(), Vec<TypecheckError>> {
+    let mut errors = Vec::new();
+    for ir in irs {
+        match &ir.kind {
+            ir @ IRKind::Define { .. } => {
+                match check_define(&ir) {
+                    Ok(()) => (),
+                    Err(e) => errors.push(e),
+                }
+            }
+            _ => {}
+        }
+    }
+    if errors.is_empty() { Ok(()) }
+    else { Err(errors) }
+}
+
+#[macro_export]
+macro_rules! return_err {
+    ($kind:expr, $span:expr) => {{
+        return Err(TypecheckError {
+            kind: $kind,
+            span: $span.clone()
+        });
+    }};
+}
+
+/// Check the types of the definitions.
+/// This is done by checking the type of the value against the type hint.
+/// 
+/// # Examples
+/// ```sml
+/// let x: int = 1; -- Correct
+/// 
+/// let x: string = 1; -- Incorrect
+/// ```
+fn check_define(ir: &IRKind) -> Result<(), TypecheckError> {
+    match ir {
+        IRKind::Define {
+            type_hint,
+            value,
+            span,
+            ..
+        } => {
+            match &**value {
+                IRKind::Value { value } => {
+                    match value {
+                        Value::Int(_) => {
+                            if type_hint != "number" {
+                                return_err!(
+                                    TypecheckErrorKind::DefinitionTypeMismatch {
+                                        type_specified: type_hint.to_string(),
+                                        type_found: "number".to_string(),
+                                    },
+                                    span.clone()
+                                );
+                            }
+                        }
+                        Value::String(_) => {
+                            if type_hint != "string" {
+                                return_err!(
+                                    TypecheckErrorKind::DefinitionTypeMismatch {
+                                        type_specified: type_hint.to_string(),
+                                        type_found: "string".to_string(),
+                                    },
+                                    span.clone()
+                                );
+                            }
+                        }
+                        Value::Boolean(_) => {
+                            if type_hint != "boolean" {
+                                return_err!(
+                                    TypecheckErrorKind::DefinitionTypeMismatch {
+                                        type_specified: type_hint.to_string(),
+                                        type_found: "boolean".to_string(),
+                                    },
+                                    span.clone()
+                                );
+                            }
+                        }
+                        // TODO: other types
+                        _ => {}
+                    }
+                }
+                // TODO: other (right-hand side) IRKinds
+                _ => {}
+            }
+        }
+        _ => unreachable!()
+    }
+    Ok(())
 }
\ No newline at end of file
diff --git a/example/err/define_wrong_type.hz b/example/err/define_wrong_type.hz
new file mode 100644
index 0000000..ced8320
--- /dev/null
+++ b/example/err/define_wrong_type.hz
@@ -0,0 +1,3 @@
+let foo: int = "123";
+let bar: string = 69;
+let baz: bool = "true";
\ No newline at end of file