diff --git a/.changeset/cypher-set-param-nullability.md b/.changeset/cypher-set-param-nullability.md
new file mode 100644
index 0000000..063b0d3
--- /dev/null
+++ b/.changeset/cypher-set-param-nullability.md
@@ -0,0 +1,7 @@
+---
+"@evryg/effect-cypher-codegen": minor
+---
+
+Infer parameter nullability for `SET` clauses
+
+`QueryAnalyzer` now types parameters bound via a `SET` clause (`MATCH (n:Label {...}) SET n.prop = $param`), in addition to node-pattern property maps and `IN` list expressions. A param assigned to an optional vertex property is typed `T | null` (so callers can pass `null` to clear it), while one assigned to a mandatory property stays non-nullable. Map-merge assignments (`SET n += $map`) are unaffected, and params whose left-hand side cannot be resolved to a schema property keep the previous non-nullable `String` fallback.
diff --git a/packages/cypher-codegen/src/frontend/QueryAnalyzer.node.unit.test.ts b/packages/cypher-codegen/src/frontend/QueryAnalyzer.node.unit.test.ts
index f2f94b8..d635bcd 100644
--- a/packages/cypher-codegen/src/frontend/QueryAnalyzer.node.unit.test.ts
+++ b/packages/cypher-codegen/src/frontend/QueryAnalyzer.node.unit.test.ts
@@ -200,6 +200,45 @@ describe("analyzeQuery — param nullability", () => {
   })
 })
 
+describe("analyzeQuery — SET-clause param nullability", () => {
+  it("marks a SET param bound to an optional vertex property as nullable", () => {
+    // Method.visibility is optional in the schema fixture
+    const cypher = "MATCH (m:Method {id: $id}) SET m.visibility = $vis RETURN m.id AS id"
+    const result = analyzeQuery(cypher, schema)
+    expect(result.params).toEqual([
+      { name: "id", type: "String", nullable: false },
+      { name: "vis", type: "String", nullable: true }
+    ])
+  })
+
+  it("marks a SET param bound to a mandatory vertex property as non-nullable", () => {
+    // Method.name is mandatory in the schema fixture
+    const cypher = "MATCH (m:Method {id: $id}) SET m.name = $nm RETURN m.id AS id"
+    const result = analyzeQuery(cypher, schema)
+    expect(result.params).toEqual([
+      { name: "id", type: "String", nullable: false },
+      { name: "nm", type: "String", nullable: false }
+    ])
+  })
+
+  it("types each item of a multi-property SET independently", () => {
+    const cypher = "MATCH (m:Method {id: $id}) SET m.visibility = $vis, m.name = $nm RETURN m.id AS id"
+    const result = analyzeQuery(cypher, schema)
+    expect(result.params).toEqual([
+      { name: "id", type: "String", nullable: false },
+      { name: "vis", type: "String", nullable: true },
+      { name: "nm", type: "String", nullable: false }
+    ])
+  })
+
+  it("does not double-count a param constrained in both a MATCH pattern and a SET", () => {
+    // Method.visibility is optional → nullable, and appears once despite two usages
+    const cypher = "MATCH (m:Method {visibility: $v}) SET m.visibility = $v RETURN m.id AS id"
+    const result = analyzeQuery(cypher, schema)
+    expect(result.params).toEqual([{ name: "v", type: "String", nullable: true }])
+  })
+})
+
 describe("analyzeQuery — WITH rebinding", () => {
   it("tracks variables through WITH clause", () => {
     const cypher = `MATCH (c:Class)
diff --git a/packages/cypher-codegen/src/frontend/QueryAnalyzer.ts b/packages/cypher-codegen/src/frontend/QueryAnalyzer.ts
index c7cc777..1f1a860 100644
--- a/packages/cypher-codegen/src/frontend/QueryAnalyzer.ts
+++ b/packages/cypher-codegen/src/frontend/QueryAnalyzer.ts
@@ -13,6 +13,7 @@ import {
   PatternElemContext,
   ReadingStatementContext,
   RelationDetailContext,
+  SetItemContext,
   UnwindStContext,
   UpdatingStatementContext,
   WithStContext
@@ -633,6 +634,34 @@ function extractParams(tree: ReturnType<typeof parse>, schema: GraphSchema): Arr
     paramUsages.push({ paramName, label, property, isInClause: true })
   })
 
+  // Pass 3: Walk SET items of the form `<var>.<prop> = $param`, mirroring Pass 1.
+  // Only the `propertyExpression ASSIGN expression` alternative is handled; `SET r += $map`
+  // (map-merge) uses the `symbol ADD_ASSIGN expression` alternative, whose propertyExpression()
+  // is null, so it is naturally excluded — that map param is a separate feature.
+  walkTree(tree, SetItemContext, (item) => {
+    const propExpr = item.propertyExpression()
+    if (!propExpr) return
+
+    // LHS must be a simple `var.prop` (single property segment).
+    const names = propExpr.name()
+    if (names.length !== 1) return
+    const varName = propExpr.atom().getText()
+    const property = names[0]!.getText()
+
+    const expr = item.expression()
+    if (!expr) return
+    const paramCtx = findParameter(expr)
+    if (!paramCtx) return
+    const paramSym = paramCtx.symbol()
+    if (!paramSym) return
+    const paramName = paramSym.getText()
+    if (seenParams.has(paramName)) return
+    seenParams.add(paramName)
+
+    const label = varLabels.get(varName)
+    paramUsages.push({ paramName, label, property })
+  })
+
   return paramUsages.map((usage) => {
     if (usage.label && usage.property) {
       const resolved = lookupParamType(schema, usage.label, usage.property)