diff --git a/src/ir/gen/conversions.rs b/src/ir/gen/conversions.rs
index 62b3af7..0261dd9 100644
--- a/src/ir/gen/conversions.rs
+++ b/src/ir/gen/conversions.rs
@@ -3,10 +3,11 @@
 //! This module provides trait implementations and helper functions to convert
 //! AST-level type representations (`ast::TypeSpecifier`, `ast::VarDecl`,
 //! `ast::VarDef`, `ast::VarDeclStmt`) into their corresponding IR-level
-//! data types (`Dtype`).
+//! data types (`Dtype`), and AST function declarations (`ast::FnDecl`)
+//! into IR function signatures ([`FunctionType`]).
 
 use crate::ast;
-use crate::ir::types::Dtype;
+use crate::ir::types::{Dtype, FunctionType};
 
 /// Converts an optional AST type specifier into the corresponding base IR data type (`Dtype`).
 ///
@@ -79,11 +80,12 @@ impl From<&ast::TypeSpecifier> for Dtype {
 }
 
 // ---------------------------------------------------------------------------
-// `TryFrom` trait implementations: AST declarations -> IR Dtype
+// `TryFrom` trait implementations: AST declarations -> IR types
 // ---------------------------------------------------------------------------
 //
-// These are fallible conversions because certain combinations (e.g., struct
-// definitions with initializers) are not supported and produce an error.
+// These are fallible conversions because certain combinations (e.g. struct
+// definitions with initializers, array parameters in function signatures)
+// are not supported and produce an error.
 
 /// Converts a variable declaration (`VarDecl`) to its IR data type.
 ///
@@ -130,3 +132,54 @@ impl TryFrom<&ast::VarDeclStmt> for Dtype {
         }
     }
 }
+
+/// Lowers an AST function declaration into a [`FunctionType`].
+///
+/// Besides the straightforward type conversion, this enforces two
+/// language rules that the back-end relies on:
+///
+/// 1. Array parameters are rejected with
+///    [`crate::ir::Error::ArrayParameterNotAllowed`] — TeaLang requires
+///    arrays to be passed by reference (`&[T]`).
+/// 2. Return types are whitelisted to `void` and `i32`.  Struct returns
+///    are grammatically legal but not yet implemented in the AArch64
+///    back-end; allowing them here would produce IR that can't be
+///    lowered, so they are rejected up-front with
+///    [`crate::ir::Error::UnsupportedReturnType`].
+impl TryFrom<&ast::FnDecl> for FunctionType {
+    type Error = crate::ir::Error;
+
+    fn try_from(decl: &ast::FnDecl) -> Result<Self, Self::Error> {
+        let return_dtype = decl
+            .return_dtype
+            .as_ref()
+            .map_or(Dtype::Void, Dtype::from);
+
+        match &return_dtype {
+            Dtype::Void | Dtype::I32 => {}
+            _ => {
+                return Err(crate::ir::Error::UnsupportedReturnType {
+                    symbol: decl.identifier.clone(),
+                    dtype: return_dtype,
+                });
+            }
+        }
+
+        let mut arguments = Vec::new();
+        if let Some(params) = &decl.param_decl {
+            for p in &params.decls {
+                let id = p.identifier.clone();
+                let dtype = Dtype::try_from(p)?;
+                if matches!(&dtype, Dtype::Array { .. }) {
+                    return Err(crate::ir::Error::ArrayParameterNotAllowed { symbol: id });
+                }
+                arguments.push((id, dtype));
+            }
+        }
+
+        Ok(Self {
+            return_dtype,
+            arguments,
+        })
+    }
+}
diff --git a/src/ir/types.rs b/src/ir/types.rs
index bc98b4d..b393361 100644
--- a/src/ir/types.rs
+++ b/src/ir/types.rs
@@ -1,4 +1,3 @@
-use crate::ast;
 use std::fmt::{self, Display, Formatter};
 
 #[derive(Clone, PartialEq, Debug)]
@@ -79,53 +78,3 @@ pub struct FunctionType {
     pub arguments: Vec<(String, Dtype)>,
 }
 
-impl TryFrom<&ast::FnDecl> for FunctionType {
-    type Error = crate::ir::Error;
-
-    /// Lowers an AST function declaration into a [`FunctionType`].
-    ///
-    /// Besides the straightforward type conversion, this enforces two
-    /// language rules that the back-end relies on:
-    ///
-    /// 1. Array parameters are rejected with
-    ///    [`crate::ir::Error::ArrayParameterNotAllowed`] — TeaLang requires
-    ///    arrays to be passed by reference (`&[T]`).
-    /// 2. Return types are whitelisted to `void` and `i32`.  Struct returns
-    ///    are grammatically legal but not yet implemented in the AArch64
-    ///    back-end; allowing them here would produce IR that can't be
-    ///    lowered, so they are rejected up-front with
-    ///    [`crate::ir::Error::UnsupportedReturnType`].
-    fn try_from(decl: &ast::FnDecl) -> Result<Self, Self::Error> {
-        let return_dtype = decl
-            .return_dtype
-            .as_ref()
-            .map_or(Dtype::Void, Dtype::from);
-
-        match &return_dtype {
-            Dtype::Void | Dtype::I32 => {}
-            _ => {
-                return Err(crate::ir::Error::UnsupportedReturnType {
-                    symbol: decl.identifier.clone(),
-                    dtype: return_dtype,
-                });
-            }
-        }
-
-        let mut arguments = Vec::new();
-        if let Some(params) = &decl.param_decl {
-            for p in &params.decls {
-                let id = p.identifier.clone();
-                let dtype = Dtype::try_from(p)?;
-                if matches!(&dtype, Dtype::Array { .. }) {
-                    return Err(crate::ir::Error::ArrayParameterNotAllowed { symbol: id });
-                }
-                arguments.push((id, dtype));
-            }
-        }
-
-        Ok(Self {
-            return_dtype,
-            arguments,
-        })
-    }
-}