diff --git a/pkg/runtime/golang/golang.go b/pkg/runtime/golang/golang.go
index 6059faef34..141edb7fc9 100644
--- a/pkg/runtime/golang/golang.go
+++ b/pkg/runtime/golang/golang.go
@@ -3,6 +3,7 @@ package golang
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"io"
 	"log/slog"
 	"os"
@@ -130,6 +131,20 @@ func (r *Runtime) Run(ctx context.Context, input *runtime.RunInput) (runtime.Wor
 	}, nil
 }
 
+func (r *Runtime) ValidateHandler(input *runtime.BuildInput) error {
+	if input.Handler != "" {
+		if info, err := os.Stat(input.Handler); err != nil || !info.IsDir() {
+			return fmt.Errorf("handler not found: %v", input.Handler)
+		}
+	}
+
+	_, err := fs.FindUp(input.Handler, "go.mod")
+	if err != nil {
+		return fmt.Errorf("handler not found: could not find go.mod for handler %v", input.Handler)
+	}
+	return nil
+}
+
 func (r *Runtime) ShouldRebuild(functionID string, file string) bool {
 	if !strings.HasSuffix(file, ".go") {
 		return false
diff --git a/pkg/runtime/node/build.go b/pkg/runtime/node/build.go
index c3bc6fbf19..abfed46426 100644
--- a/pkg/runtime/node/build.go
+++ b/pkg/runtime/node/build.go
@@ -41,7 +41,7 @@ func (r *Runtime) Build(ctx context.Context, input *runtime.BuildInput) (*runtim
 
 	file, ok := r.getFile(input)
 	if !ok {
-		return nil, fmt.Errorf("Handler not found: %v", input.Handler)
+		return nil, fmt.Errorf("handler not found: %v", input.Handler)
 	}
 
 	isESM := true
diff --git a/pkg/runtime/node/node.go b/pkg/runtime/node/node.go
index f35f237b25..86b2528afc 100644
--- a/pkg/runtime/node/node.go
+++ b/pkg/runtime/node/node.go
@@ -3,6 +3,7 @@ package node
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"io"
 	"log/slog"
 	"os"
@@ -242,15 +243,12 @@ func (r *Runtime) Match(runtime string) bool {
 	return strings.HasPrefix(runtime, "node")
 }
 
-func (r *Runtime) getFile(input *runtime.BuildInput) (string, bool) {
-	dir := filepath.Dir(input.Handler)
-	fileSplit := strings.Split(filepath.Base(input.Handler), ".")
+func findHandlerFile(rootDir string, handler string) (string, bool) {
+	dir := filepath.Dir(handler)
+	fileSplit := strings.Split(filepath.Base(handler), ".")
 	base := strings.Join(fileSplit[:len(fileSplit)-1], ".")
 	for _, ext := range NODE_EXTENSIONS {
-		file := filepath.Join(dir, base+ext)
-		if !filepath.IsAbs(file) {
-			file = filepath.Join(path.ResolveRootDir(input.CfgPath), file)
-		}
+		file := filepath.Join(rootDir, dir, base+ext)
 		if _, err := os.Stat(file); err == nil {
 			return file, true
 		}
@@ -258,6 +256,22 @@ func (r *Runtime) getFile(input *runtime.BuildInput) (string, bool) {
 	return "", false
 }
 
+func (r *Runtime) getFile(input *runtime.BuildInput) (string, bool) {
+	return findHandlerFile(path.ResolveRootDir(input.CfgPath), input.Handler)
+}
+
+func (r *Runtime) ValidateHandler(input *runtime.BuildInput) error {
+	rootDir := path.ResolveRootDir(input.CfgPath)
+	if input.Bundle != "" {
+		rootDir = input.Bundle
+	}
+	_, ok := findHandlerFile(rootDir, input.Handler)
+	if !ok {
+		return fmt.Errorf("handler not found: %v", input.Handler)
+	}
+	return nil
+}
+
 func (r *Runtime) ShouldRebuild(functionID string, file string) bool {
 	result, ok := r.results.Load(functionID)
 	if !ok {
diff --git a/pkg/runtime/python/python.go b/pkg/runtime/python/python.go
index eb882e7919..dba5bb6a56 100644
--- a/pkg/runtime/python/python.go
+++ b/pkg/runtime/python/python.go
@@ -175,6 +175,18 @@ func (r *PythonRuntime) Run(ctx context.Context, input *runtime.RunInput) (runti
 
 }
 
+func (r *PythonRuntime) ValidateHandler(input *runtime.BuildInput) error {
+	rootDir := path.ResolveRootDir(input.CfgPath)
+	if input.Bundle != "" {
+		rootDir = input.Bundle
+	}
+	_, err := findHandlerFile(rootDir, input.Handler)
+	if err != nil {
+		return fmt.Errorf("handler not found: %v", input.Handler)
+	}
+	return nil
+}
+
 func (r *PythonRuntime) ShouldRebuild(functionID string, file string) bool {
 	// Assume that the build is always stale. We could do a better job here but bc of how the build
 	// process actually works its not a slowdown as the real slow part is starting the python interpreter
@@ -382,25 +394,25 @@ func (r *PythonRuntime) CreateBuildAsset(ctx context.Context, input *runtime.Bui
 	}
 }
 
-func (r *PythonRuntime) getFile(input *runtime.BuildInput) (string, error) {
-	slog.Info("looking for python handler file", "handler", input.Handler)
-
-	dir := filepath.Dir(input.Handler)
-	base := strings.TrimSuffix(filepath.Base(input.Handler), filepath.Ext(input.Handler))
-	rootDir := path.ResolveRootDir(input.CfgPath)
+func findHandlerFile(rootDir string, handler string) (string, error) {
+	dir := filepath.Dir(handler)
+	base := strings.TrimSuffix(filepath.Base(handler), filepath.Ext(handler))
 
-	// Look for .py file
 	pythonFile := filepath.Join(rootDir, dir, base+".py")
 	if _, err := os.Stat(pythonFile); err == nil {
 		return pythonFile, nil
 	}
 
-	// No Python file found for the handler
 	return "", fmt.Errorf("could not find Python file '%s.py' in directory '%s'",
 		base,
 		filepath.Join(rootDir, dir))
 }
 
+func (r *PythonRuntime) getFile(input *runtime.BuildInput) (string, error) {
+	slog.Info("looking for python handler file", "handler", input.Handler)
+	return findHandlerFile(path.ResolveRootDir(input.CfgPath), input.Handler)
+}
+
 func copyFile(src, dst string) error {
 	srcFile, err := os.Open(src)
 	if err != nil {
diff --git a/pkg/runtime/runtime.go b/pkg/runtime/runtime.go
index b8436aa6cd..08232e730d 100644
--- a/pkg/runtime/runtime.go
+++ b/pkg/runtime/runtime.go
@@ -20,6 +20,7 @@ type Runtime interface {
 	Build(ctx context.Context, input *BuildInput) (*BuildOutput, error)
 	Run(ctx context.Context, input *RunInput) (Worker, error)
 	ShouldRebuild(functionID string, path string) bool
+	ValidateHandler(input *BuildInput) error
 }
 
 type Worker interface {
@@ -100,6 +101,13 @@ func (c *Collection) Build(ctx context.Context, input *BuildInput) (*BuildOutput
 
 	if input.Bundle != "" {
 		out = input.Bundle
+		runtime, ok := c.Runtime(input.Runtime)
+		if !ok {
+			return nil, fmt.Errorf("runtime not found: %v", input.Runtime)
+		}
+		if err := runtime.ValidateHandler(input); err != nil {
+			return nil, err
+		}
 		result = &BuildOutput{
 			Handler: input.Handler,
 			Errors:  []string{},
diff --git a/pkg/runtime/runtime_test.go b/pkg/runtime/runtime_test.go
index 69dc5f169d..60719b5089 100644
--- a/pkg/runtime/runtime_test.go
+++ b/pkg/runtime/runtime_test.go
@@ -26,6 +26,9 @@ func (m *mockRuntime) Run(ctx context.Context, input *runtime.RunInput) (runtime
 func (m *mockRuntime) ShouldRebuild(functionID string, path string) bool {
 	return false
 }
+func (m *mockRuntime) ValidateHandler(input *runtime.BuildInput) error {
+	return nil
+}
 
 func TestBuildInputOut(t *testing.T) {
 	cfgPath := filepath.Join("/project", "sst.config.ts")
diff --git a/pkg/runtime/rust/rust.go b/pkg/runtime/rust/rust.go
index 367cd649a2..37082c5b71 100644
--- a/pkg/runtime/rust/rust.go
+++ b/pkg/runtime/rust/rust.go
@@ -81,6 +81,10 @@ func (r *Runtime) Build(ctx context.Context, input *runtime.BuildInput) (*runtim
 	var properties Properties
 	json.Unmarshal(input.Properties, &properties)
 
+	if err := r.ValidateHandler(input); err != nil {
+		return nil, err
+	}
+
 	// split handler into path and function name
 	parts := strings.Split(input.Handler, ".")
 	handler := strings.Join(parts[:len(parts)-1], ".")
@@ -194,6 +198,26 @@ func (r *Runtime) Run(ctx context.Context, input *runtime.RunInput) (runtime.Wor
 	}, nil
 }
 
+func (r *Runtime) ValidateHandler(input *runtime.BuildInput) error {
+	parts := strings.Split(input.Handler, ".")
+	handler := strings.Join(parts[:len(parts)-1], ".")
+
+	if handler != "" {
+		if info, err := os.Stat(handler); err != nil || !info.IsDir() {
+			return fmt.Errorf("handler not found: %v", input.Handler)
+		}
+	}
+
+	_, err := fs.FindUp(handler, "cargo.toml")
+	if err != nil {
+		_, err = fs.FindUp(handler, "Cargo.toml")
+		if err != nil {
+			return fmt.Errorf("handler not found: could not find Cargo.toml for handler %v", input.Handler)
+		}
+	}
+	return nil
+}
+
 func (r *Runtime) ShouldRebuild(functionID string, file string) bool {
 	// copied from go
 	if !strings.HasSuffix(file, ".rs") {
diff --git a/pkg/runtime/worker/worker.go b/pkg/runtime/worker/worker.go
index 52d39d4726..1d84c6add2 100644
--- a/pkg/runtime/worker/worker.go
+++ b/pkg/runtime/worker/worker.go
@@ -179,11 +179,11 @@ func (w *Runtime) Match(runtime string) bool {
 	return runtime == "worker"
 }
 
-func (w *Runtime) getFile(input *runtime.BuildInput) (string, bool) {
-	dir := filepath.Dir(input.Handler)
-	base := strings.Split(filepath.Base(input.Handler), ".")[0]
+func findHandlerFile(rootDir string, handler string) (string, bool) {
+	dir := filepath.Dir(handler)
+	base := strings.Split(filepath.Base(handler), ".")[0]
 	for _, ext := range node.NODE_EXTENSIONS {
-		file := filepath.Join(path.ResolveRootDir(input.CfgPath), dir, base+ext)
+		file := filepath.Join(rootDir, dir, base+ext)
 		if _, err := os.Stat(file); err == nil {
 			return file, true
 		}
@@ -191,6 +191,22 @@ func (w *Runtime) getFile(input *runtime.BuildInput) (string, bool) {
 	return "", false
 }
 
+func (w *Runtime) getFile(input *runtime.BuildInput) (string, bool) {
+	return findHandlerFile(path.ResolveRootDir(input.CfgPath), input.Handler)
+}
+
+func (r *Runtime) ValidateHandler(input *runtime.BuildInput) error {
+	rootDir := path.ResolveRootDir(input.CfgPath)
+	if input.Bundle != "" {
+		rootDir = input.Bundle
+	}
+	_, ok := findHandlerFile(rootDir, input.Handler)
+	if !ok {
+		return fmt.Errorf("handler not found: %v", input.Handler)
+	}
+	return nil
+}
+
 func (r *Runtime) ShouldRebuild(functionID string, file string) bool {
 	r.lock.RLock()
 	result, ok := r.results[functionID]
diff --git a/pkg/server/runtime/runtime.go b/pkg/server/runtime/runtime.go
index 0e91a3212c..ba95d7bd7b 100644
--- a/pkg/server/runtime/runtime.go
+++ b/pkg/server/runtime/runtime.go
@@ -2,6 +2,7 @@ package runtime
 
 import (
 	"context"
+	"fmt"
 	"net/rpc"
 
 	"github.com/sst/sst/v3/pkg/bus"
@@ -24,6 +25,14 @@ func (r *Runtime) Build(input *runtime.BuildInput, output *runtime.BuildOutput)
 }
 
 func (r *Runtime) AddTarget(input *runtime.BuildInput, output *bool) error {
+	input.CfgPath = r.project.PathConfig()
+	rt, ok := r.project.Runtime.Runtime(input.Runtime)
+	if !ok {
+		return fmt.Errorf("runtime not found: %v", input.Runtime)
+	}
+	if err := rt.ValidateHandler(input); err != nil {
+		return err
+	}
 	bus.Publish(input)
 	*output = true
 	return nil