diff --git a/.github/workflows/client.yml b/.github/workflows/client.yml
index 91964f2..0287730 100644
--- a/.github/workflows/client.yml
+++ b/.github/workflows/client.yml
@@ -34,7 +34,7 @@ jobs:
         run: go build ./...
 
       - name: Install gotestsum
-        run: go install gotest.tools/gotestsum@v1.12.0
+        run: go install gotest.tools/gotestsum@v1.13.0
 
       - name: Run Go tests
         run: gotestsum
diff --git a/pkg/cmd/flag/flag_big_int_test.go b/pkg/cmd/flag/flag_big_int_test.go
index 7f90a28..d753aef 100644
--- a/pkg/cmd/flag/flag_big_int_test.go
+++ b/pkg/cmd/flag/flag_big_int_test.go
@@ -1,9 +1,8 @@
 package flag
 
 import (
-	"fmt"
+	"errors"
 	"math/big"
-	"reflect"
 	"testing"
 
 	pflag "github.com/spf13/pflag"
@@ -25,9 +24,9 @@ func TestBigIntVarFlag_Set(t *testing.T) {
 		},
 		"invalid value": {
 			value: "100k",
-			expectedError: fmt.Errorf(
-				"invalid argument \"100k\" for \"--%s\" flag: failed to parse as big.Int: 100k",
-				bigIntFlagName,
+			expectedError: errors.New(
+				"invalid argument \"100k\" for \"--" + bigIntFlagName +
+					"\" flag: failed to parse as big.Int: 100k",
 			),
 			expectedValue: defaultValue,
 		},
@@ -43,7 +42,7 @@ func TestBigIntVarFlag_Set(t *testing.T) {
 
 			err := flags.Set(bigIntFlagName, test.value)
 
-			if !reflect.DeepEqual(test.expectedError, err) {
+			if errorMessage(err) != errorMessage(test.expectedError) {
 				t.Errorf(
 					"unexpected error\nexpected: %v\nactual:   %v\n",
 					test.expectedError,
diff --git a/pkg/cmd/flag/flag_helpers_test.go b/pkg/cmd/flag/flag_helpers_test.go
new file mode 100644
index 0000000..53c0fc8
--- /dev/null
+++ b/pkg/cmd/flag/flag_helpers_test.go
@@ -0,0 +1,12 @@
+package flag
+
+// errorMessage returns err.Error() or "" if err is nil. Used to compare error
+// equality by message string rather than by concrete type, since pflag wraps
+// underlying errors with fmt.Errorf("...: %w", inner) — the rendered message
+// stays stable across pflag versions but the concrete type does not.
+func errorMessage(err error) string {
+	if err == nil {
+		return ""
+	}
+	return err.Error()
+}
diff --git a/pkg/cmd/flag/flag_wei_test.go b/pkg/cmd/flag/flag_wei_test.go
index 498d0d4..bfadce0 100644
--- a/pkg/cmd/flag/flag_wei_test.go
+++ b/pkg/cmd/flag/flag_wei_test.go
@@ -1,9 +1,8 @@
 package flag
 
 import (
-	"fmt"
+	"errors"
 	"math/big"
-	"reflect"
 	"testing"
 
 	"github.com/keep-network/keep-common/pkg/chain/ethereum"
@@ -37,16 +36,16 @@ func TestWeiVarFlag_Set(t *testing.T) {
 		},
 		"value with invalid comma delimiter": {
 			value: "3,5 ether",
-			expectedError: fmt.Errorf(
-				"invalid argument \"3,5 ether\" for \"--%s\" flag: failed to parse value: [3,5 ether]",
-				flagName,
+			expectedError: errors.New(
+				"invalid argument \"3,5 ether\" for \"--" + flagName +
+					"\" flag: failed to parse value: [3,5 ether]",
 			),
 		},
 		"value with invalid unit": {
 			value: "10 bei",
-			expectedError: fmt.Errorf(
-				"invalid argument \"10 bei\" for \"--%s\" flag: invalid unit: bei; please use one of: ether, gwei, wei",
-				flagName,
+			expectedError: errors.New(
+				"invalid argument \"10 bei\" for \"--" + flagName +
+					"\" flag: invalid unit: bei; please use one of: ether, gwei, wei",
 			),
 		},
 	}
@@ -61,7 +60,7 @@ func TestWeiVarFlag_Set(t *testing.T) {
 
 			err := flags.Set(flagName, test.value)
 
-			if !reflect.DeepEqual(test.expectedError, err) {
+			if errorMessage(err) != errorMessage(test.expectedError) {
 				t.Errorf(
 					"unexpected error\nexpected: %v\nactual:   %v\n",
 					test.expectedError,