diff --git a/kaptan-spec/src/lib.rs b/kaptan-spec/src/lib.rs
index 3869fe3..0911393 100644
--- a/kaptan-spec/src/lib.rs
+++ b/kaptan-spec/src/lib.rs
@@ -1,9 +1,10 @@
-use proc_macro::{Literal, Punct, Spacing, TokenStream, TokenTree};
+use proc_macro::{Literal, TokenStream, TokenTree};
 
 #[proc_macro_attribute]
 pub fn spec(attr: TokenStream, item: TokenStream) -> TokenStream {
     match parse_spec_path(attr) {
-        Ok(path) => expand_spec_guard(&path, item),
+        Ok(path) if is_module_item(&item) => expand_spec_guard(&path, item),
+        Ok(_) => compile_error("`#[spec]` may only be applied to a module"),
         Err(message) => compile_error(&message),
     }
 }
@@ -12,13 +13,12 @@ fn parse_spec_path(attr: TokenStream) -> Result<String, String> {
     let tokens: Vec<TokenTree> = attr.into_iter().collect();
 
     match tokens.as_slice() {
-        [TokenTree::Literal(path)] if is_string_literal(path) => Ok(path.to_string()),
-        [
-            TokenTree::Ident(name),
-            TokenTree::Punct(eq),
-            TokenTree::Literal(path),
-        ] if name.to_string() == "path" && is_equals(eq) && is_string_literal(path) => {
-            Ok(path.to_string())
+        [TokenTree::Literal(path)] if is_string_literal(path) => {
+            if has_spec_suffix(path) {
+                Ok(path.to_string())
+            } else {
+                Err("spec path must end in `.spec.md`; use #[spec(\"file.spec.md\")]".into())
+            }
         }
         [] => Err("missing spec path; use #[spec(\"file.spec.md\")]".into()),
         _ => Err("invalid spec attribute; use #[spec(\"file.spec.md\")]".into()),
@@ -28,11 +28,20 @@ fn parse_spec_path(attr: TokenStream) -> Result<String, String> {
 fn is_string_literal(literal: &Literal) -> bool {
     let value = literal.to_string();
 
-    value.starts_with('"') || value.starts_with("r\"") || value.starts_with("r#")
+    value.starts_with('"') && value.ends_with('"')
 }
 
-fn is_equals(punct: &Punct) -> bool {
-    punct.as_char() == '=' && punct.spacing() == Spacing::Alone
+fn has_spec_suffix(literal: &Literal) -> bool {
+    literal
+        .to_string()
+        .strip_suffix('"')
+        .is_some_and(|path| path.ends_with(".spec.md"))
+}
+
+fn is_module_item(item: &TokenStream) -> bool {
+    item.clone().into_iter().any(
+        |token| matches!(token, TokenTree::Ident(identifier) if identifier.to_string() == "mod"),
+    )
 }
 
 fn expand_spec_guard(path: &str, item: TokenStream) -> TokenStream {
diff --git a/kaptan-spec/tests/spec_macro.rs b/kaptan-spec/tests/spec_macro.rs
index 14a3505..a62807c 100644
--- a/kaptan-spec/tests/spec_macro.rs
+++ b/kaptan-spec/tests/spec_macro.rs
@@ -5,7 +5,13 @@ fn accepts_existing_sidecar_spec() {
 }
 
 #[test]
-fn rejects_missing_sidecar_spec() {
+fn rejects_invalid_spec_uses() {
     let tests = trybuild::TestCases::new();
+
+    tests.compile_fail("tests/ui/fail_missing_argument.rs");
+    tests.compile_fail("tests/ui/fail_legacy_named_argument.rs");
+    tests.compile_fail("tests/ui/fail_non_string_argument.rs");
+    tests.compile_fail("tests/ui/fail_invalid_suffix.rs");
     tests.compile_fail("tests/ui/fail_missing_sidecar.rs");
+    tests.compile_fail("tests/ui/fail_non_module_item.rs");
 }
diff --git a/kaptan-spec/tests/ui/fail_invalid_suffix.rs b/kaptan-spec/tests/ui/fail_invalid_suffix.rs
new file mode 100644
index 0000000..293e9cd
--- /dev/null
+++ b/kaptan-spec/tests/ui/fail_invalid_suffix.rs
@@ -0,0 +1,6 @@
+use kaptan_spec::spec;
+
+#[spec("flight_core_contract.md")]
+struct InvalidSuffix;
+
+fn main() {}
\ No newline at end of file
diff --git a/kaptan-spec/tests/ui/fail_invalid_suffix.stderr b/kaptan-spec/tests/ui/fail_invalid_suffix.stderr
new file mode 100644
index 0000000..512489b
--- /dev/null
+++ b/kaptan-spec/tests/ui/fail_invalid_suffix.stderr
@@ -0,0 +1,7 @@
+error: spec path must end in `.spec.md`; use #[spec("file.spec.md")]
+ --> tests/ui/fail_invalid_suffix.rs:3:1
+  |
+3 | #[spec("flight_core_contract.md")]
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  |
+  = note: this error originates in the attribute macro `spec` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/kaptan-spec/tests/ui/fail_legacy_named_argument.rs b/kaptan-spec/tests/ui/fail_legacy_named_argument.rs
new file mode 100644
index 0000000..c5c539c
--- /dev/null
+++ b/kaptan-spec/tests/ui/fail_legacy_named_argument.rs
@@ -0,0 +1,6 @@
+use kaptan_spec::spec;
+
+#[spec(path = "flight_core_contract.spec.md")]
+struct LegacyNamedArgument;
+
+fn main() {}
\ No newline at end of file
diff --git a/kaptan-spec/tests/ui/fail_legacy_named_argument.stderr b/kaptan-spec/tests/ui/fail_legacy_named_argument.stderr
new file mode 100644
index 0000000..8e45974
--- /dev/null
+++ b/kaptan-spec/tests/ui/fail_legacy_named_argument.stderr
@@ -0,0 +1,7 @@
+error: invalid spec attribute; use #[spec("file.spec.md")]
+ --> tests/ui/fail_legacy_named_argument.rs:3:1
+  |
+3 | #[spec(path = "flight_core_contract.spec.md")]
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  |
+  = note: this error originates in the attribute macro `spec` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/kaptan-spec/tests/ui/fail_missing_argument.rs b/kaptan-spec/tests/ui/fail_missing_argument.rs
new file mode 100644
index 0000000..4b62f4f
--- /dev/null
+++ b/kaptan-spec/tests/ui/fail_missing_argument.rs
@@ -0,0 +1,6 @@
+use kaptan_spec::spec;
+
+#[spec]
+struct MissingArgument;
+
+fn main() {}
\ No newline at end of file
diff --git a/kaptan-spec/tests/ui/fail_missing_argument.stderr b/kaptan-spec/tests/ui/fail_missing_argument.stderr
new file mode 100644
index 0000000..d2c56d3
--- /dev/null
+++ b/kaptan-spec/tests/ui/fail_missing_argument.stderr
@@ -0,0 +1,7 @@
+error: missing spec path; use #[spec("file.spec.md")]
+ --> tests/ui/fail_missing_argument.rs:3:1
+  |
+3 | #[spec]
+  | ^^^^^^^
+  |
+  = note: this error originates in the attribute macro `spec` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/kaptan-spec/tests/ui/fail_missing_sidecar.rs b/kaptan-spec/tests/ui/fail_missing_sidecar.rs
index 1cddb67..9057817 100644
--- a/kaptan-spec/tests/ui/fail_missing_sidecar.rs
+++ b/kaptan-spec/tests/ui/fail_missing_sidecar.rs
@@ -1,8 +1,7 @@
 use kaptan_spec::spec;
 
 #[spec("fail_missing_sidecar.spec.md")]
-struct MissingSpec;
+mod missing_spec {}
 
 fn main() {
-    let _ = core::mem::size_of::<MissingSpec>();
 }
\ No newline at end of file
diff --git a/kaptan-spec/tests/ui/fail_non_module_item.rs b/kaptan-spec/tests/ui/fail_non_module_item.rs
new file mode 100644
index 0000000..16bd7bb
--- /dev/null
+++ b/kaptan-spec/tests/ui/fail_non_module_item.rs
@@ -0,0 +1,6 @@
+use kaptan_spec::spec;
+
+#[spec("flight_core_contract.spec.md")]
+struct FlightCore;
+
+fn main() {}
\ No newline at end of file
diff --git a/kaptan-spec/tests/ui/fail_non_module_item.stderr b/kaptan-spec/tests/ui/fail_non_module_item.stderr
new file mode 100644
index 0000000..7825be9
--- /dev/null
+++ b/kaptan-spec/tests/ui/fail_non_module_item.stderr
@@ -0,0 +1,7 @@
+error: `#[spec]` may only be applied to a module
+ --> tests/ui/fail_non_module_item.rs:3:1
+  |
+3 | #[spec("flight_core_contract.spec.md")]
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  |
+  = note: this error originates in the attribute macro `spec` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/kaptan-spec/tests/ui/fail_non_string_argument.rs b/kaptan-spec/tests/ui/fail_non_string_argument.rs
new file mode 100644
index 0000000..7a61a0d
--- /dev/null
+++ b/kaptan-spec/tests/ui/fail_non_string_argument.rs
@@ -0,0 +1,6 @@
+use kaptan_spec::spec;
+
+#[spec(42)]
+struct NonStringArgument;
+
+fn main() {}
\ No newline at end of file
diff --git a/kaptan-spec/tests/ui/fail_non_string_argument.stderr b/kaptan-spec/tests/ui/fail_non_string_argument.stderr
new file mode 100644
index 0000000..ff595e6
--- /dev/null
+++ b/kaptan-spec/tests/ui/fail_non_string_argument.stderr
@@ -0,0 +1,7 @@
+error: invalid spec attribute; use #[spec("file.spec.md")]
+ --> tests/ui/fail_non_string_argument.rs:3:1
+  |
+3 | #[spec(42)]
+  | ^^^^^^^^^^^
+  |
+  = note: this error originates in the attribute macro `spec` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/kaptan-spec/tests/ui/flight_core_contract.rs b/kaptan-spec/tests/ui/flight_core_contract.rs
index 399782f..705ebd9 100644
--- a/kaptan-spec/tests/ui/flight_core_contract.rs
+++ b/kaptan-spec/tests/ui/flight_core_contract.rs
@@ -1,9 +1,8 @@
 use kaptan_spec::spec;
 
 #[spec("flight_core_contract.spec.md")]
-struct FlightCore;
+mod flight_core {}
 
 fn main() {
-    let size = core::mem::size_of::<FlightCore>();
-    assert_eq!(size, 0);
+    assert_eq!(core::mem::size_of::<()>(), 0);
 }
\ No newline at end of file