diff --git a/Dockerfile b/Dockerfile
index 91213152..4bd0886e 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -4,7 +4,7 @@ WORKDIR /src
 RUN apk add make git
 RUN make
 
-FROM debian:stable-20230612
+FROM debian:stable-20230703
 RUN apt-get update --yes && \
     apt-get install --no-install-recommends --yes git ca-certificates && \
     rm -rf /var/lib/apt/lists/*
diff --git a/internal/checks/base.go b/internal/checks/base.go
index 4d7c183e..d51f49d2 100644
--- a/internal/checks/base.go
+++ b/internal/checks/base.go
@@ -2,6 +2,7 @@ package checks
 
 import (
 	"context"
+	"encoding/json"
 	"errors"
 	"fmt"
 
@@ -78,6 +79,10 @@ func ParseSeverity(s string) (Severity, error) {
 	}
 }
 
+func (s Severity) MarshalJSON() ([]byte, error) {
+	return json.Marshal(s.String())
+}
+
 const (
 	// Information doesn't count as a problem, it's a comment
 	Information Severity = iota
diff --git a/internal/reporter/json_test.go b/internal/reporter/json_test.go
index 59040436..7a30b33d 100644
--- a/internal/reporter/json_test.go
+++ b/internal/reporter/json_test.go
@@ -44,6 +44,6 @@ func TestJSONReporter(t *testing.T) {
 	defer jsonFile.Close()
 	byteValue, err := io.ReadAll(jsonFile)
 	require.NoError(t, err, "Error reading json")
-	expected := "[{\"reportedPath\":\"\",\"sourcePath\":\"foo.txt\",\"rule\":{\"name\":\"sum errors\",\"type\":\"recording\"},\"problem\":{\"Fragment\":\"syntax error\",\"Lines\":[2],\"Reporter\":\"mock\",\"Text\":\"syntax error\",\"Severity\":3},\"owner\":\"\"}]"
+	expected := "[{\"reportedPath\":\"\",\"sourcePath\":\"foo.txt\",\"rule\":{\"name\":\"sum errors\",\"type\":\"recording\"},\"problem\":{\"Fragment\":\"syntax error\",\"Lines\":[2],\"Reporter\":\"mock\",\"Text\":\"syntax error\",\"Severity\":\"Fatal\"},\"owner\":\"\"}]"
 	require.Equal(t, expected, string(byteValue))
 }