diff --git a/CHANGELOG.md b/CHANGELOG.md
index c41367c..2a32e84 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
 ## Unreleased
 
+BUG FIXES:
+
+* RouterCallImpl: fix decoding the response from vshard.storage.call
+* RouterCallImpl: do not return nil error when StorageCallAssertError has happened
+
 FEATURES:
 
 * Added etcd v2 topology provider implementation (#16)
diff --git a/api.go b/api.go
index 52f87ec..d7b1666 100644
--- a/api.go
+++ b/api.go
@@ -73,8 +73,9 @@ func (r *Router) RouterCallImpl(ctx context.Context,
 	opts CallOpts,
 	fnc string,
 	args interface{}) (interface{}, StorageResultTypedFunc, error) {
+
 	if bucketID > r.cfg.TotalBucketCount {
-		return nil, nil, fmt.Errorf("bucket is unreachable: bucket id is out of range")
+		return nil, nil, fmt.Errorf("bucket id is out of range: %d (total %d)", bucketID, r.cfg.TotalBucketCount)
 	}
 
 	if opts.Timeout == 0 {
@@ -117,10 +118,12 @@ func (r *Router) RouterCallImpl(ctx context.Context,
 			continue
 		}
 
-		r.log().Info(ctx, fmt.Sprintf("try call replicaset %s", rs.info.Name))
+		r.log().Info(ctx, fmt.Sprintf("try call %s on replicaset %s for bucket %d", fnc, rs.info.Name, bucketID))
 
 		future := rs.conn.Do(req, opts.PoolMode)
-		respData, err := future.Get()
+
+		var respData []interface{}
+		respData, err = future.Get()
 		if err != nil {
 			r.log().Error(ctx, fmt.Sprintf("got future error: %s", err))
 			r.metrics().RetryOnCall("future_get_error")
@@ -128,8 +131,13 @@ func (r *Router) RouterCallImpl(ctx context.Context,
 			continue
 		}
 
+		r.log().Debug(ctx, fmt.Sprintf("got call result response data %s", respData))
+
 		if len(respData) < 1 {
-			err = fmt.Errorf("invalid length of response data: must be >1, current: %d", len(respData))
+			// vshard.storage.call(func) returns up to two values:
+			// - true/false
+			// - func result, omitted if func does not return anything
+			err = fmt.Errorf("invalid length of response data: must be >= 1, current: %d", len(respData))
 
 			r.log().Error(ctx, err.Error())
 
@@ -140,11 +148,18 @@ func (r *Router) RouterCallImpl(ctx context.Context,
 		if respData[0] == nil {
 			vshardErr := &StorageCallVShardError{}
 
-			err = mapstructure.Decode(respData[1], vshardErr)
+			if len(respData) < 2 {
+				err = fmt.Errorf("unexpected response length when respData[0] == nil: %d", len(respData))
+			} else {
+				err = mapstructure.Decode(respData[1], vshardErr)
+			}
+
 			if err != nil {
 				r.metrics().RetryOnCall("internal_error")
 
-				r.log().Error(ctx, fmt.Sprintf("cant decode vhsard err by trarantool with err: %s; continue try", err))
+				err = fmt.Errorf("cant decode vhsard err by trarantool with err: %s; continue try", err)
+
+				r.log().Error(ctx, err.Error())
 				continue
 			}
 
@@ -175,19 +190,33 @@ func (r *Router) RouterCallImpl(ctx context.Context,
 		if !isVShardRespOk { // error
 			errorResp := &StorageCallAssertError{}
 
-			err = future.GetTyped(&[]interface{}{&isVShardRespOk, errorResp})
+			// Since we got respData[0] == false, it means that assert has happened
+			// while executing user-defined function on vshard storage.
+			// In this case, vshard storage must return a pair: false, error.
+			if len(respData) < 2 {
+				err = fmt.Errorf("protocol violation: unexpected response length when respData[0] == false: %d", len(respData))
+			} else {
+				err = future.GetTyped(&[]interface{}{&isVShardRespOk, errorResp})
+			}
+
 			if err != nil {
+				// Either protocol has been violated or decoding has failed.
 				err = fmt.Errorf("cant get typed vshard err with err: %s", err)
+			} else {
+				// StorageCallAssertError successfully has been decoded.
+				err = errorResp
 			}
 
-			err = errorResp
+			continue
 		}
 
 		r.metrics().RequestDuration(time.Since(timeStart), true, false)
 
-		r.log().Debug(ctx, fmt.Sprintf("got call result response data %s", respData))
-
 		return respData[1:], func(result interface{}) error {
+			if len(respData) < 2 {
+				return nil
+			}
+
 			var stub interface{}
 
 			return future.GetTyped(&[]interface{}{&stub, result})
diff --git a/vshard.go b/vshard.go
index 35ee282..a3e7021 100644
--- a/vshard.go
+++ b/vshard.go
@@ -207,7 +207,7 @@ func validateCfg(cfg Config) error {
 	}
 
 	if cfg.TotalBucketCount == 0 {
-		return fmt.Errorf("bucket count must be grather then 0")
+		return fmt.Errorf("bucket count must be greater than 0")
 	}
 
 	return nil