diff --git a/internal/analyzer/schemas.go b/internal/analyzer/schemas.go
index 3bb8396..20c0f14 100644
--- a/internal/analyzer/schemas.go
+++ b/internal/analyzer/schemas.go
@@ -179,11 +179,25 @@ func (a *Analyzer) convertAllOf(goName string, schema *highbase.Schema, nullable
 		IsNullable:  nullable,
 	}
 
-	// Collect required fields from the parent schema.
+	// Collect required fields from the parent schema. Every entry's requirements
+	// apply to the same value, so they are read before any property is built and
+	// a property required by one entry is required by the struct.
 	requiredSet := make(map[string]bool, len(schema.Required))
 	for _, r := range schema.Required {
 		requiredSet[r] = true
 	}
+	for _, proxy := range schema.AllOf {
+		if entry, err := proxy.BuildSchema(); err == nil && entry != nil {
+			for _, r := range entry.Required {
+				requiredSet[r] = true
+			}
+		}
+	}
+
+	// Entries compose one value, so a property more than one of them declares is
+	// one field. Appending a field per declaration gives two with the same JSON
+	// tag, which encoding/json resolves by ignoring both.
+	declared := make(map[string]bool)
 
 	for _, proxy := range schema.AllOf {
 		ref := proxy.GetReference()
@@ -209,11 +223,6 @@ func (a *Analyzer) convertAllOf(goName string, schema *highbase.Schema, nullable
 			continue
 		}
 
-		// Merge required from the allOf entry.
-		for _, r := range entrySchema.Required {
-			requiredSet[r] = true
-		}
-
 		if entrySchema.Properties == nil {
 			continue
 		}
@@ -227,6 +236,10 @@ func (a *Analyzer) convertAllOf(goName string, schema *highbase.Schema, nullable
 				continue
 			}
 
+			if declared[propName] {
+				continue
+			}
+			declared[propName] = true
 			td.Fields = addField(td.Fields, a.convertProperty(goName, propName, propSchema, requiredSet[propName], multipartBody))
 		}
 	}
diff --git a/internal/analyzer/schemas_allof_property_test.go b/internal/analyzer/schemas_allof_property_test.go
index 4aee7b9..02201ea 100644
--- a/internal/analyzer/schemas_allof_property_test.go
+++ b/internal/analyzer/schemas_allof_property_test.go
@@ -191,3 +191,83 @@ func TestAllOfProperty_MultipartBodyKeepsItsFileParts(t *testing.T) {
 		t.Errorf("fields = %+v, want the embedded Meta beside the file", body.Fields)
 	}
 }
+
+const allOfRedeclaredSpec = `openapi: 3.1.0
+info: { title: t, version: "1" }
+paths: {}
+components:
+  schemas:
+    Forkee:
+      allOf:
+        - type: object
+          properties:
+            name: { type: string }
+            archived: { type: boolean }
+            size: { type: integer }
+        - type: object
+          properties:
+            name: { type: string }
+            archived: { type: boolean }
+          required: [name]
+    Composed:
+      allOf:
+        - $ref: "#/components/schemas/Base"
+        - type: object
+          properties:
+            id: { type: string }
+    Base:
+      type: object
+      properties:
+        id: { type: string }
+`
+
+// allOf entries compose one value, so a property more than one declares is one
+// field. Two fields carrying one JSON tag is not just untidy: encoding/json
+// resolves that by ignoring both, so the property stops round-tripping.
+func TestAllOf_RedeclaredPropertyIsOneField(t *testing.T) {
+	_, typeMap := analyzeSpec(t, allOfRedeclaredSpec)
+
+	forkee := typeMap["Forkee"]
+	if forkee == nil {
+		t.Fatal("Forkee not found")
+	}
+
+	seen := map[string]int{}
+	for _, f := range forkee.Fields {
+		seen[f.JSONName]++
+	}
+	for _, prop := range []string{"name", "archived"} {
+		if seen[prop] != 1 {
+			t.Errorf("%s appears %d times, want once", prop, seen[prop])
+		}
+	}
+	if len(forkee.Fields) != 3 {
+		t.Errorf("fields = %+v, want name, archived, and size", forkee.Fields)
+	}
+
+	// A property one entry requires is required by the struct, whichever entry
+	// declared it first.
+	for _, f := range forkee.Fields {
+		if f.JSONName == "name" && !f.Required {
+			t.Errorf("name = %+v, want required: the second entry requires it", f)
+		}
+	}
+}
+
+// A property beside an embedded type is a different case: they live at
+// different depths, so Go shadows one with the other and the JSON tags do not
+// collide.
+func TestAllOf_PropertyBesideAnEmbedIsKept(t *testing.T) {
+	_, typeMap := analyzeSpec(t, allOfRedeclaredSpec)
+
+	composed := typeMap["Composed"]
+	if composed == nil {
+		t.Fatal("Composed not found")
+	}
+	if len(composed.Fields) != 2 {
+		t.Fatalf("fields = %+v, want the embed and the property", composed.Fields)
+	}
+	if !composed.Fields[0].Embedded || composed.Fields[1].JSONName != "id" {
+		t.Errorf("fields = %+v, want Base embedded beside id", composed.Fields)
+	}
+}
diff --git a/internal/generator/e2e_combinations_test.go b/internal/generator/e2e_combinations_test.go
index 2077198..ab42930 100644
--- a/internal/generator/e2e_combinations_test.go
+++ b/internal/generator/e2e_combinations_test.go
@@ -79,6 +79,7 @@ func TestE2E_Combinations(t *testing.T) {
 		{"operations.go", "params.Either", "a union-typed parameter"},
 		{"errors.go", "func (e *ProblemResponse) Error() string", "a typed error wrapper"},
 		{"errors.go", "e.Detail.Detail", "a message field found by its conventional name"},
+		{"types.go", "Name string `json:\"name\"`", "a property two allOf entries declare, required by one"},
 	} {
 		if !containsCollapsed(byName[want.file], want.decl) {
 			t.Errorf("%s is missing %s (%s)", want.file, want.why, want.decl)
diff --git a/testdata/combinations.yaml b/testdata/combinations.yaml
index d2bd8fa..7a5bfcc 100644
--- a/testdata/combinations.yaml
+++ b/testdata/combinations.yaml
@@ -187,6 +187,18 @@ components:
             kind: { const: gadget }
             gears: { type: integer }
           required: [kind, gears]
+    # Two entries that redeclare properties: one field each, or encoding/json
+    # ignores both of them.
+    Refined:
+      allOf:
+        - type: object
+          properties:
+            name: { type: string }
+            size: { type: integer }
+        - type: object
+          properties:
+            name: { type: string }
+          required: [name]
     Alert:
       type: object
       properties:
@@ -199,6 +211,7 @@ components:
           type: object
           patternProperties:
             "^x-": { type: string }
+        refined: { $ref: "#/components/schemas/Refined" }
       required: [id]
     Problem:
       type: object