diff --git a/packages/mermaid/src/defaultConfig.ts b/packages/mermaid/src/defaultConfig.ts
index 28454e353..62b361cff 100644
--- a/packages/mermaid/src/defaultConfig.ts
+++ b/packages/mermaid/src/defaultConfig.ts
@@ -50,7 +50,6 @@ const config: Partial<MermaidConfig> = {
     ...defaultConfigJson.gantt,
     tickInterval: undefined,
     useWidth: undefined, // can probably be removed since `configKeys` already includes this
-    weekday: 'sunday', // the sane default is a monday, but it's set to sunday for legacy reasons
   },
   c4: {
     ...defaultConfigJson.c4,
diff --git a/packages/mermaid/src/schemas/config.schema.yaml b/packages/mermaid/src/schemas/config.schema.yaml
index 306aab2cc..8bebd68cf 100644
--- a/packages/mermaid/src/schemas/config.schema.yaml
+++ b/packages/mermaid/src/schemas/config.schema.yaml
@@ -1455,6 +1455,7 @@ $defs: # JSON Schema definition (maybe we should move these to a seperate file)
       - axisFormat
       - useMaxWidth
       - topAxis
+      - weekday
     properties:
       titleTopMargin:
         $ref: '#/$defs/GitGraphDiagramConfig/properties/titleTopMargin'
@@ -1544,6 +1545,20 @@ $defs: # JSON Schema definition (maybe we should move these to a seperate file)
         default: ''
         # Allow any string for typescript backwards compatibility (fix in Mermaid v10)
         tsType: 'string | "compact"'
+      weekday:
+        description: |
+          On which day a week-based interval should start
+        type: string
+        enum:
+          - monday
+          - tuesday
+          - wednesday
+          - thursday
+          - friday
+          - saturday
+          - sunday
+        # the sane default is a monday, but it's set to sunday for legacy reasons
+        default: sunday
 
   SequenceDiagramConfig:
     title: Sequence Diagram Config