diff --git a/find_step.go b/find_step.go
index 361c664..bf09d24 100644
--- a/find_step.go
+++ b/find_step.go
@@ -9,11 +9,11 @@ import (
 func (r *Runner) findStep(t *testing.T, step *messages.PickleStep) *stepDef {
 	t.Helper()
 
-	for _, def := range r.stepDefs {
-		matches := def.regex.FindSubmatch([]byte(step.Text))
-		if len(matches) != 0 {
-			return def
-		}
+	r.stepDefsMutex.RLock()
+	def := findSubmatch(t, step.Text, r.stepDefs)
+	r.stepDefsMutex.RUnlock()
+	if def != nil {
+		return def
 	}
 
 	sig := guessMethodSig(step)
@@ -30,3 +30,16 @@ func (r *Runner) findStep(t *testing.T, step *messages.PickleStep) *stepDef {
 
 	return nil
 }
+
+func findSubmatch(t *testing.T, stepText string, stepDefs []*stepDef) *stepDef {
+	t.Helper()
+
+	for _, def := range stepDefs {
+		matches := def.regex.FindSubmatch([]byte(stepText))
+		if len(matches) != 0 {
+			return def
+		}
+	}
+
+	return nil
+}
\ No newline at end of file
diff --git a/runner.go b/runner.go
index 2795328..4a848d9 100644
--- a/runner.go
+++ b/runner.go
@@ -2,6 +2,7 @@ package gocuke
 
 import (
 	"reflect"
+	"sync"
 	"testing"
 
 	messages "github.com/cucumber/messages/go/v22"
@@ -17,6 +18,7 @@ type Runner struct {
 	paths                []string
 	parallel             bool
 	stepDefs             []*stepDef
+	stepDefsMutex 	  	 *sync.RWMutex
 	haveSuggestion       map[string]bool
 	suggestions          []methodSig
 	supportedSpecialArgs map[reflect.Type]specialArgGetter
@@ -84,6 +86,7 @@ func NewRunner(t *testing.T, suiteType interface{}) *Runner {
 			},
 		},
 		suiteUsesRapid: false,
+		stepDefsMutex: &sync.RWMutex{},
 	}
 
 	r.registerSuite(suiteType)
diff --git a/simple_test.go b/simple_test.go
index 97b0b31..35123b8 100644
--- a/simple_test.go
+++ b/simple_test.go
@@ -34,7 +34,6 @@ func TestSimpleNonPointer(t *testing.T) {
 	gocuke.
 		NewRunner(t, simpleSuiteNP{}).
 		Path("examples/simple/simple.feature").
-		NonParallel().
 		Run()
 }
 
diff --git a/step_def.go b/step_def.go
index a3446a1..e6e1df5 100644
--- a/step_def.go
+++ b/step_def.go
@@ -54,7 +54,9 @@ func (r *Runner) Step(step interface{}, definition interface{}) *Runner {
 
 func (r *Runner) addStepDef(t *testing.T, exp *regexp.Regexp, definition reflect.Value) *stepDef {
 	t.Helper()
+	defer r.stepDefsMutex.Unlock()
 
+	r.stepDefsMutex.Lock()
 	def := r.newStepDefOrHook(t, exp, definition)
 	r.stepDefs = append(r.stepDefs, def)
 	return def