diff --git a/crates/cli/tests/interface-types.rs b/crates/cli/tests/interface-types.rs
index a5d8d9a7..462dccf0 100644
--- a/crates/cli/tests/interface-types.rs
+++ b/crates/cli/tests/interface-types.rs
@@ -12,7 +12,7 @@ fn main() -> Result<()> {
     let dir = env::current_dir()?.join("tests/interface-types");
     for entry in dir.read_dir()? {
         let path = entry?.path();
-        if path.extension().and_then(|s| s.to_str()) != Some("wit") {
+        if path.extension().and_then(|s| s.to_str()) != Some("wat") {
             continue;
         }
         if let Some(filter) = &filter {
diff --git a/crates/cli/tests/interface-types/anyref.wit b/crates/cli/tests/interface-types/anyref.wat
similarity index 100%
rename from crates/cli/tests/interface-types/anyref.wit
rename to crates/cli/tests/interface-types/anyref.wat
diff --git a/crates/cli/tests/interface-types/defer-call.wit b/crates/cli/tests/interface-types/defer-call.wat
similarity index 100%
rename from crates/cli/tests/interface-types/defer-call.wit
rename to crates/cli/tests/interface-types/defer-call.wat
diff --git a/crates/cli/tests/interface-types/empty.wit b/crates/cli/tests/interface-types/empty.wat
similarity index 100%
rename from crates/cli/tests/interface-types/empty.wit
rename to crates/cli/tests/interface-types/empty.wat
diff --git a/crates/cli/tests/interface-types/integers.wit b/crates/cli/tests/interface-types/integers.wat
similarity index 100%
rename from crates/cli/tests/interface-types/integers.wit
rename to crates/cli/tests/interface-types/integers.wat
diff --git a/crates/cli/tests/interface-types/memory-to-string.wit b/crates/cli/tests/interface-types/memory-to-string.wat
similarity index 100%
rename from crates/cli/tests/interface-types/memory-to-string.wit
rename to crates/cli/tests/interface-types/memory-to-string.wat
diff --git a/crates/cli/tests/interface-types/no-wasm.wit b/crates/cli/tests/interface-types/no-wasm.wat
similarity index 100%
rename from crates/cli/tests/interface-types/no-wasm.wit
rename to crates/cli/tests/interface-types/no-wasm.wat
diff --git a/crates/cli/tests/interface-types/string-to-memory.wit b/crates/cli/tests/interface-types/string-to-memory.wat
similarity index 100%
rename from crates/cli/tests/interface-types/string-to-memory.wit
rename to crates/cli/tests/interface-types/string-to-memory.wat
diff --git a/crates/cli/tests/reference.rs b/crates/cli/tests/reference.rs
index 855f52a2..4df55ec0 100644
--- a/crates/cli/tests/reference.rs
+++ b/crates/cli/tests/reference.rs
@@ -109,8 +109,8 @@ fn runtest(test: &Path) -> Result<()> {
     if interface_types {
         let wasm = td.path().join("reference_test.wasm");
         wit_validator::validate(&fs::read(&wasm)?)?;
-        let wit = sanitize_wasm(&wasm)?;
-        assert_same(&wit, &test.with_extension("wit"))?;
+        let wat = sanitize_wasm(&wasm)?;
+        assert_same(&wat, &test.with_extension("wat"))?;
     } else {
         let js = fs::read_to_string(td.path().join("reference_test.js"))?;
         assert_same(&js, &test.with_extension("js"))?;
diff --git a/crates/cli/tests/reference/interface-types-anyref.wit b/crates/cli/tests/reference/interface-types-anyref.wat
similarity index 100%
rename from crates/cli/tests/reference/interface-types-anyref.wit
rename to crates/cli/tests/reference/interface-types-anyref.wat
diff --git a/crates/cli/tests/reference/interface-types-empty.wit b/crates/cli/tests/reference/interface-types-empty.wat
similarity index 100%
rename from crates/cli/tests/reference/interface-types-empty.wit
rename to crates/cli/tests/reference/interface-types-empty.wat
diff --git a/crates/cli/tests/reference/interface-types-integers.wit b/crates/cli/tests/reference/interface-types-integers.wat
similarity index 100%
rename from crates/cli/tests/reference/interface-types-integers.wit
rename to crates/cli/tests/reference/interface-types-integers.wat
diff --git a/crates/cli/tests/reference/interface-types-interop.wit b/crates/cli/tests/reference/interface-types-interop.wat
similarity index 100%
rename from crates/cli/tests/reference/interface-types-interop.wit
rename to crates/cli/tests/reference/interface-types-interop.wat
diff --git a/crates/cli/tests/reference/interface-types-strings.wit b/crates/cli/tests/reference/interface-types-strings.wat
similarity index 100%
rename from crates/cli/tests/reference/interface-types-strings.wit
rename to crates/cli/tests/reference/interface-types-strings.wat