diff --git a/assured/assured_endpoints.go b/assured/assured_endpoints.go
index dce296f..09109a8 100644
--- a/assured/assured_endpoints.go
+++ b/assured/assured_endpoints.go
@@ -3,6 +3,7 @@ package assured
 import (
 	"context"
 	"errors"
+	"sync"
 
 	"github.com/go-kit/kit/endpoint"
 	kitlog "github.com/go-kit/kit/log"
@@ -13,6 +14,7 @@ type AssuredEndpoints struct {
 	logger       kitlog.Logger
 	assuredCalls map[string][]*Call
 	madeCalls    map[string][]*Call
+	sync.Mutex
 }
 
 // NewAssuredEndpoints creates a new instance of assured endpoints
@@ -37,8 +39,11 @@ func (a *AssuredEndpoints) WrappedEndpoint(handler func(context.Context, *Call)
 
 // GivenEndpoint is used to stub out a call for a given path
 func (a *AssuredEndpoints) GivenEndpoint(ctx context.Context, call *Call) (interface{}, error) {
+	a.Lock()
 	a.assuredCalls[call.ID()] = append(a.assuredCalls[call.ID()], call)
+	a.Unlock()
 	a.logger.Log("message", "assured call set", "path", call.ID())
+
 	return call, nil
 }
 
@@ -49,11 +54,11 @@ func (a *AssuredEndpoints) WhenEndpoint(ctx context.Context, call *Call) (interf
 		return nil, errors.New("No assured calls")
 	}
 
+	a.Lock()
 	a.madeCalls[call.ID()] = append(a.madeCalls[call.ID()], call)
-
 	assured := a.assuredCalls[call.ID()][0]
-
 	a.assuredCalls[call.ID()] = append(a.assuredCalls[call.ID()][1:], assured)
+	a.Unlock()
 
 	return assured, nil
 }
@@ -65,8 +70,10 @@ func (a *AssuredEndpoints) VerifyEndpoint(ctx context.Context, call *Call) (inte
 
 //ClearEndpoint is used to clear a specific assured call
 func (a *AssuredEndpoints) ClearEndpoint(ctx context.Context, call *Call) (interface{}, error) {
+	a.Lock()
 	delete(a.assuredCalls, call.ID())
 	delete(a.madeCalls, call.ID())
+	a.Unlock()
 	a.logger.Log("message", "cleared calls for path", "path", call.ID())
 
 	return nil, nil
@@ -74,8 +81,10 @@ func (a *AssuredEndpoints) ClearEndpoint(ctx context.Context, call *Call) (inter
 
 //ClearAllEndpoint is used to clear all assured calls
 func (a *AssuredEndpoints) ClearAllEndpoint(ctx context.Context, i interface{}) (interface{}, error) {
+	a.Lock()
 	a.assuredCalls = map[string][]*Call{}
 	a.madeCalls = map[string][]*Call{}
+	a.Unlock()
 	a.logger.Log("message", "cleared all calls")
 
 	return nil, nil