diff --git a/.buildbot.sh b/.buildbot.sh
index 11b67f2a..cb6361e3 100644
--- a/.buildbot.sh
+++ b/.buildbot.sh
@@ -34,6 +34,8 @@ cargo +alloy test --release
 cargo +alloy run  -- --cp SOM/Smalltalk SOM/TestSuite/TestHarness.som
 cargo +alloy run --release -- --cp SOM/Smalltalk SOM/TestSuite/TestHarness.som
 
+cargo +alloy run --release -- --cp SOM/Smalltalk:lang_tests hello_world1
+
 cd SOM
 cargo +alloy run --release -- \
   --cp Smalltalk:TestSuite:SomSom/src/compiler:SomSom/src/vm:SomSom/src/vmobjects:SomSom/src/interpreter:SomSom/src/primitives \
diff --git a/src/main.rs b/src/main.rs
index 9b04d1ea..1987cf03 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -30,12 +30,13 @@ fn usage(prog: &str) -> ! {
         .file_name()
         .map(|x| x.to_str().unwrap_or("yksom"))
         .unwrap_or("yksom");
-    writeln!(
-        &mut stderr(),
-        "Usage: {} [-h] --cp <path> <file.som> [-- <arg_1> [... <arg_n>]]",
-        leaf
-    )
-    .ok();
+    error(&format!(
+        "Usage: {leaf} [-h] --cp <path> <file.som> [-- <arg_1> [... <arg_n>]]"
+    ));
+}
+
+fn error(msg: &str) -> ! {
+    stderr().write_all(msg.as_bytes()).ok();
     process::exit(1)
 }
 
@@ -56,18 +57,39 @@ fn main() {
         usage(prog);
     }
 
-    let src_path = &Path::new(&matches.free[0]).canonicalize().unwrap();
-    let mut cp = match src_path.parent() {
-        Some(p) => vec![p.to_owned()],
-        None => vec![],
+    let mut cp: Vec<_> = matches
+        .opt_str("cp")
+        .unwrap()
+        .split(":")
+        .map(|x| PathBuf::from_str(x).unwrap())
+        .collect();
+
+    let mut src_path = Path::new(&matches.free[0]).to_owned();
+    if !src_path.is_file() && src_path.extension().is_none() {
+        for d in &cp {
+            let mut p = PathBuf::new();
+            p.push(d);
+            p.push(&matches.free[0]);
+            p.set_extension("som");
+            if p.is_file() {
+                src_path = p;
+            }
+        }
+        if !src_path.is_file() {
+            error(&format!(
+                "{} does not exist or is not a file",
+                &matches.free[0]
+            ));
+        }
+    }
+    let src_path = match src_path.canonicalize() {
+        Ok(s) => s,
+        Err(e) => error(&format!("Can't canonicalise {}: {}", &matches.free[0], e)),
     };
-    cp.extend(
-        matches
-            .opt_str("cp")
-            .unwrap()
-            .split(":")
-            .map(|x| PathBuf::from_str(x).unwrap()),
-    );
+
+    if let Some(p) = src_path.parent() {
+        cp.insert(0, p.to_owned());
+    }
 
     let mut vm = VM::new(cp);
     let system = vm.get_global_or_nil("system");