diff --git a/internal/core/error.go b/internal/core/error.go
index 455b1b1..3578767 100644
--- a/internal/core/error.go
+++ b/internal/core/error.go
@@ -33,6 +33,8 @@ func ToGrpcError(err error) error {
 		return status.Error(codes.FailedPrecondition, err.Error())
 	case errors.Is(err, ErrNotFound):
 		return status.Error(codes.NotFound, err.Error())
+	case errors.Is(err, ErrUnknownEntryType):
+		return status.Error(codes.Internal, err.Error())
 	case errors.Is(err, ErrReplicateQuorumUnreachable):
 		return status.Error(codes.Unavailable, err.Error())
 	default:
diff --git a/internal/core/error_test.go b/internal/core/error_test.go
new file mode 100644
index 0000000..04fe1d3
--- /dev/null
+++ b/internal/core/error_test.go
@@ -0,0 +1,67 @@
+package core
+
+import (
+	"context"
+	"testing"
+
+	"github.com/pkg/errors"
+	"github.com/stretchr/testify/require"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+)
+
+func TestToGrpcError(t *testing.T) {
+	tests := []struct {
+		name     string
+		inputErr error
+		wantCode codes.Code
+	}{
+		{"nil error", nil, codes.OK},
+		{"context canceled", context.Canceled, codes.Canceled},
+		{"context deadline exceeded", context.DeadlineExceeded, codes.DeadlineExceeded},
+		{"empty key error", ErrEmptyKey, codes.InvalidArgument},
+		{"not leader error", ErrNotLeader, codes.FailedPrecondition},
+		{"not found error", ErrNotFound, codes.NotFound},
+		{"replicate quorum unreachable", ErrReplicateQuorumUnreachable, codes.Unavailable},
+		{"unknown error", errors.New("generic error"), codes.Internal},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotErr := ToGrpcError(tt.inputErr)
+
+			if tt.inputErr == nil {
+				require.Nil(t, gotErr, "expected nil error but got %v", gotErr)
+				return
+			}
+
+			gotStatus, _ := status.FromError(gotErr)
+			require.Equal(t, tt.wantCode, gotStatus.Code(), "unexpected gRPC code")
+		})
+	}
+}
+
+func FuzzToGrpcError(f *testing.F) {
+	f.Add("random error")
+	f.Add("context canceled")
+	f.Add("context deadline exceeded")
+	f.Add("empty key")
+	f.Add("not leader")
+	f.Add("not found")
+	f.Add("unknown entry type")
+	f.Add("replicate quorum unreachable")
+
+	f.Fuzz(func(t *testing.T, input string) {
+		inputErr := errors.New(input)
+		gotErr := ToGrpcError(inputErr)
+
+		if inputErr == nil {
+			require.Nil(t, gotErr, "expected nil error but got %v", gotErr)
+			return
+		}
+
+		gotStatus, _ := status.FromError(gotErr)
+		require.NotNil(t, gotStatus, "status should never be nil")
+		require.NotEqual(t, codes.OK, gotStatus.Code(), "unexpected gRPC code")
+	})
+}