diff --git a/types/diagnostics.go b/types/diagnostics.go
index 41d18b7..3ae0955 100644
--- a/types/diagnostics.go
+++ b/types/diagnostics.go
@@ -10,6 +10,28 @@ import (
 // Data is lost when doing a json marshal.
 type Diagnostics hcl.Diagnostics
 
+func (d *Diagnostics) UnmarshalJSON(data []byte) error {
+	cpy := make([]FriendlyDiagnostic, 0)
+	if err := json.Unmarshal(data, &cpy); err != nil {
+		return err
+	}
+
+	*d = make(Diagnostics, 0, len(cpy))
+	for _, diag := range cpy {
+		severity := hcl.DiagError
+		if diag.Severity == DiagnosticSeverityWarning {
+			severity = hcl.DiagWarning
+		}
+
+		*d = append(*d, &hcl.Diagnostic{
+			Severity: severity,
+			Summary:  diag.Summary,
+			Detail:   diag.Detail,
+		})
+	}
+	return nil
+}
+
 func (d Diagnostics) MarshalJSON() ([]byte, error) {
 	cpy := make([]FriendlyDiagnostic, 0, len(d))
 	for _, diag := range d {
diff --git a/types/diagnostics_test.go b/types/diagnostics_test.go
new file mode 100644
index 0000000..82a4845
--- /dev/null
+++ b/types/diagnostics_test.go
@@ -0,0 +1,36 @@
+package types_test
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/hashicorp/hcl/v2"
+	"github.com/stretchr/testify/require"
+
+	"github.com/coder/preview/types"
+)
+
+func TestDiagnosticsJSON(t *testing.T) {
+
+	diags := types.Diagnostics{
+		{
+			Severity: hcl.DiagWarning,
+			Summary:  "Some summary",
+			Detail:   "Some detail",
+		},
+		{
+			Severity: hcl.DiagError,
+			Summary:  "Some summary",
+			Detail:   "Some detail",
+		},
+	}
+
+	data, err := json.Marshal(diags)
+	require.NoError(t, err, "marshal")
+
+	var newDiags types.Diagnostics
+	err = json.Unmarshal(data, &newDiags)
+	require.NoError(t, err, "unmarshal")
+
+	require.Equal(t, diags, newDiags)
+}