diff --git a/compiler.go b/compiler.go
index 9d6bcb39..4e1973e1 100644
--- a/compiler.go
+++ b/compiler.go
@@ -3026,7 +3026,9 @@ func (c *Compiler) Optimize(optLevel, sizeLevel int, inlinerThreshold uint) {
 	defer builder.Dispose()
 	builder.SetOptLevel(optLevel)
 	builder.SetSizeLevel(sizeLevel)
-	builder.UseInlinerWithThreshold(inlinerThreshold)
+	if inlinerThreshold != 0 {
+		builder.UseInlinerWithThreshold(inlinerThreshold)
+	}
 	builder.AddCoroutinePassesToExtensionPoints()
 
 	// Run function passes for each function.
diff --git a/main.go b/main.go
index e80ca392..40518f07 100644
--- a/main.go
+++ b/main.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+	"errors"
 	"flag"
 	"fmt"
 	"os"
@@ -77,11 +78,42 @@ func Compile(pkgName, runtimePath, outpath, target string, printIR, dumpSSA bool
 	return nil
 }
 
+// Run the specified package directly (using JIT or interpretation).
+func Run(pkgName string) error {
+	c, err := NewCompiler(pkgName, llvm.DefaultTargetTriple(), false)
+	if err != nil {
+		return errors.New("compiler: " + err.Error())
+	}
+	err = c.Parse(pkgName, []string{runtime.GOOS, runtime.GOARCH})
+	if err != nil {
+		return errors.New("compiler: " + err.Error())
+	}
+	if err := c.Verify(); err != nil {
+		return errors.New("compiler error: failed to verify module: " + err.Error())
+	}
+	c.Optimize(1, 0, 0) // -O1, the fastest optimization level that doesn't crash
+
+	engine, err := llvm.NewExecutionEngine(c.mod)
+	if err != nil {
+		return errors.New("interpreter setup: " + err.Error())
+	}
+	defer engine.Dispose()
+
+	main := engine.FindFunction("main")
+	if main.IsNil() {
+		return errors.New("could not find main function")
+	}
+	engine.RunFunction(main, nil)
+
+	return nil
+}
+
 func usage() {
 	fmt.Fprintf(os.Stderr, "usage: %s command [-printir] -runtime=<runtime.bc> [-target=<target>] -o <output> <input>\n", os.Args[0])
 	fmt.Fprintln(os.Stderr, "\ncommands:")
 	fmt.Fprintln(os.Stderr, "  build: compile packages and dependencies")
 	fmt.Fprintln(os.Stderr, "  help:  print this help text")
+	fmt.Fprintln(os.Stderr, "  run:   run package in an interpreter")
 	fmt.Fprintln(os.Stderr, "\nflags:")
 	flag.PrintDefaults()
 }
@@ -123,6 +155,21 @@ func main() {
 		}
 	case "help":
 		usage()
+	case "run":
+		if flag.NArg() != 1 {
+			fmt.Fprintln(os.Stderr, "No package specified.")
+			usage()
+			os.Exit(1)
+		}
+		if *target != llvm.DefaultTargetTriple() {
+			fmt.Fprintf(os.Stderr, "Cannot run %s: target triple does not match host triple.")
+			os.Exit(1)
+		}
+		err := Run(flag.Arg(0))
+		if err != nil {
+			fmt.Fprintln(os.Stderr, "error:", err)
+			os.Exit(1)
+		}
 	default:
 		fmt.Fprintln(os.Stderr, "Unknown command:", command)
 		usage()