diff --git a/packages/malloy/src/lang/composite-source-utils.ts b/packages/malloy/src/lang/composite-source-utils.ts
index 92eda2ac3f..e614857085 100644
--- a/packages/malloy/src/lang/composite-source-utils.ts
+++ b/packages/malloy/src/lang/composite-source-utils.ts
@@ -39,6 +39,7 @@ import {
   isJoinable,
   isJoined,
   isQuerySegment,
+  isRepeatedRecord,
   isSourceDef,
   isTurtle,
 } from '../model/malloy_types';
@@ -410,6 +411,7 @@ interface JoinDependency {
   path: string[];
   dependsOn: Set<string>;
   checked?: boolean;
+  onReferencesNestedData?: boolean;
 }
 
 function getJoin(
@@ -449,7 +451,12 @@ function findActiveJoins(
 
     // Add this join's path to the sorted list after its dependencies
     if (dep) {
-      sorted.push({path: dep.path});
+      const usage: FieldUsage = {path: dep.path};
+      if (dep.onReferencesNestedData) {
+        usage.onReferencesNestedData = true;
+      }
+
+      sorted.push(usage);
     }
   };
 
@@ -536,10 +543,27 @@ function expandFieldUsage(
       const joinKey = pathToKey('join', joinPath);
       const thisDep = getJoin(activeJoinGraph, joinKey, joinPath);
 
-      if (isJoined(joinDef) && !thisDep.checked) {
+      const needsTracking = isJoined(joinDef) || isRepeatedRecord(joinDef);
+      if (needsTracking && !thisDep.checked) {
         thisDep.checked = true;
+
         const joinFieldUsage = getJoinFieldUsage(joinDef, joinPath);
 
+        if (
+          joinPath.length > 1 &&
+          (isJoined(joinDef) || isRepeatedRecord(joinDef))
+        ) {
+          const parentPath = joinPath.slice(0, -1);
+          const parentKey = pathToKey('join', parentPath);
+          const parentDep = activeJoinGraph[parentKey];
+
+          // The parent join's ON expression led us to this nested structure
+          // Mark it as needing complex SQL generation
+          if (parentDep && !parentDep.onReferencesNestedData) {
+            parentDep.onReferencesNestedData = true;
+          }
+        }
+
         // Add join's field dependencies to the queue
         for (const usage of joinFieldUsage) {
           const key = pathToKey('field', usage.path);
diff --git a/packages/malloy/src/lang/test/source.spec.ts b/packages/malloy/src/lang/test/source.spec.ts
index 8a025a9f1f..77ea0ec481 100644
--- a/packages/malloy/src/lang/test/source.spec.ts
+++ b/packages/malloy/src/lang/test/source.spec.ts
@@ -1051,4 +1051,54 @@ describe('source:', () => {
       }
     }
   });
+  test('join ON expression sets onReferencesNestedData flag', () => {
+    const t = model`
+      source: usr is a extend {
+        rename: id is ai
+        dimension: email is concat(astr, ".com")
+      }
+      source: res is a extend {
+        rename: user_id is ai
+        join_one: usr on usr.id = user_id
+        dimension: usr_email is usr.email
+      }
+      source: msg is a extend {
+        rename: id is ai
+        dimension: msg_email is concat(astr, '.com')
+        join_many: res on msg_email = res.usr_email
+      }
+      run: msg -> {
+        select: *, res.usr_email
+      }
+    `;
+
+    expect(t).toTranslate();
+
+    const query = t.translator.getQuery(0);
+    expect(query).toBeDefined();
+    if (query) {
+      const firstSegment = query.pipeline[0];
+      expect(firstSegment.type).toBe('project');
+      if (firstSegment.type === 'project') {
+        expect(firstSegment.activeJoins).toBeDefined();
+
+        // Find the 'res' join in activeJoins
+        const resJoin = firstSegment.activeJoins?.find(
+          j => j.path.length === 1 && j.path[0] === 'res'
+        );
+
+        // The 'res' join should have onReferencesChildren set to true
+        // because its ON expression uses res.usr_email which expands to usr.email
+        expect(resJoin).toBeDefined();
+        expect(resJoin?.onReferencesNestedData).toBe(true);
+
+        // The 'usr' join (nested within res) should NOT have the flag
+        const usrJoin = firstSegment.activeJoins?.find(
+          j => j.path.length === 2 && j.path[0] === 'res' && j.path[1] === 'usr'
+        );
+        expect(usrJoin).toBeDefined();
+        expect(usrJoin?.onReferencesNestedData).toBeUndefined();
+      }
+    }
+  });
 });
diff --git a/packages/malloy/src/model/field_instance.ts b/packages/malloy/src/model/field_instance.ts
index 7f582be2bd..370abcd334 100644
--- a/packages/malloy/src/model/field_instance.ts
+++ b/packages/malloy/src/model/field_instance.ts
@@ -451,7 +451,8 @@ export class FieldInstanceResult implements FieldInstance {
   addStructToJoin(
     qs: QueryStruct,
     uniqueKeyRequirement: UniqueKeyRequirement
-  ): void {
+  ): JoinInstance {
+    // CHANGED: now returns JoinInstance
     const name = qs.getIdentifier();
 
     let join = this.root().joins.get(name);
@@ -460,7 +461,7 @@ export class FieldInstanceResult implements FieldInstance {
         join.uniqueKeyRequirement,
         uniqueKeyRequirement
       );
-      return;
+      return join; // CHANGED: return existing join
     }
 
     // if we have a parent, join it first.
@@ -480,6 +481,7 @@ export class FieldInstanceResult implements FieldInstance {
       join.uniqueKeyRequirement,
       uniqueKeyRequirement
     );
+    return join;
   }
 
   root(): FieldInstanceResultRoot {
diff --git a/packages/malloy/src/model/join_instance.ts b/packages/malloy/src/model/join_instance.ts
index 5c4384238e..de72263a6a 100644
--- a/packages/malloy/src/model/join_instance.ts
+++ b/packages/malloy/src/model/join_instance.ts
@@ -17,6 +17,7 @@ export class JoinInstance {
   leafiest = false;
   joinFilterConditions?: QueryFieldBoolean[];
   children: JoinInstance[] = [];
+  onReferencesNestedData?: boolean;
   constructor(
     public queryStruct: QueryStruct,
     public alias: string,
diff --git a/packages/malloy/src/model/malloy_types.ts b/packages/malloy/src/model/malloy_types.ts
index 9accd8d12b..631a38feac 100644
--- a/packages/malloy/src/model/malloy_types.ts
+++ b/packages/malloy/src/model/malloy_types.ts
@@ -1192,6 +1192,7 @@ export interface FieldUsage {
   at?: DocumentLocation;
   uniqueKeyRequirement?: UniqueKeyRequirement;
   analyticFunctionUse?: boolean;
+  onReferencesNestedData?: boolean;
 }
 
 export function bareFieldUsage(fu: FieldUsage): boolean {
diff --git a/packages/malloy/src/model/query_query.ts b/packages/malloy/src/model/query_query.ts
index aa31dac845..bf14f1ef6f 100644
--- a/packages/malloy/src/model/query_query.ts
+++ b/packages/malloy/src/model/query_query.ts
@@ -246,16 +246,22 @@ export class QueryQuery extends QueryField {
     return {as, field};
   }
 
+  // Modified addDependantPath to return the JoinInstance
   private addDependantPath(
     path: string[],
     uniqueKeyRequirement: UniqueKeyRequirement
-  ) {
+  ): JoinInstance {
     const node = this.parent.getFieldByName(path);
     const joinableParent =
       node instanceof QueryFieldStruct
         ? node.queryStruct.getJoinableParent()
         : node.parent.getJoinableParent();
-    this.rootResult.addStructToJoin(joinableParent, uniqueKeyRequirement);
+
+    // This returns the JoinInstance
+    return this.rootResult.addStructToJoin(
+      joinableParent,
+      uniqueKeyRequirement
+    );
   }
 
   private dependenciesFromFieldUsage() {
@@ -269,7 +275,10 @@ export class QueryQuery extends QueryField {
     }
 
     for (const joinUsage of this.firstSegment.activeJoins || []) {
-      this.addDependantPath(joinUsage.path, undefined);
+      const joinInstance = this.addDependantPath(joinUsage.path, undefined);
+      if (joinUsage.onReferencesNestedData) {
+        joinInstance.onReferencesNestedData = true;
+      }
     }
     for (const usage of this.firstSegment.expandedFieldUsage || []) {
       if (usage.analyticFunctionUse) {
@@ -876,11 +885,20 @@ export class QueryQuery extends QueryField {
         });
       }
 
-      if (
-        ji.children.length === 0 ||
-        conditions === undefined ||
-        !this.parent.dialect.supportsComplexFilteredSources
-      ) {
+      const needsComplexPattern =
+        ji.onReferencesNestedData || // NEW: our flag for ON conditions referencing nested data
+        (ji.children.length > 0 &&
+          conditions !== undefined &&
+          conditions.length > 0 &&
+          this.parent.dialect.supportsComplexFilteredSources);
+
+      if (!needsComplexPattern) {
+        // Simple case - direct JOIN
+        if (conditions !== undefined && conditions.length >= 1) {
+          filters = ` AND (${conditions.join(' AND ')})`;
+        }
+        s += ` ${matrixOperation} JOIN ${structSQL} AS ${ji.alias}\n  ON ${onCondition}${filters}\n`;
+      } else {
         // LTNOTE: need a check here to see the children's where: conditions are local
         //  to the source and not to any of it's joined children.
         //  In Presto, we're going to get a SQL error if in this case
@@ -894,12 +912,6 @@ export class QueryQuery extends QueryField {
         //     'Cannot join a source with a complex filter on a joined source'
         //   );
         // }
-
-        if (conditions !== undefined && conditions.length >= 1) {
-          filters = ` AND (${conditions.join(' AND ')})`;
-        }
-        s += ` ${matrixOperation} JOIN ${structSQL} AS ${ji.alias}\n  ON ${onCondition}${filters}\n`;
-      } else {
         let select = `SELECT ${ji.alias}.*`;
         let joins = '';
         for (const childJoin of ji.children) {
@@ -909,14 +921,15 @@ export class QueryQuery extends QueryField {
             getDialectFieldList(childJoin.queryStruct.structDef)
           )} AS ${childJoin.alias}`;
         }
-        select += `\nFROM ${structSQL} AS ${
-          ji.alias
-        }\n${joins}\nWHERE ${conditions?.join(' AND ')}\n`;
+        select += `\nFROM ${structSQL} AS ${ji.alias}\n${joins}`;
+        if (conditions && conditions.length > 0) {
+          select += `\nWHERE ${conditions.join(' AND ')}\n`;
+        }
         s += `${matrixOperation} JOIN (\n${indent(select)}) AS ${
           ji.alias
         }\n  ON ${onCondition}\n`;
-        return s;
       }
+      return s;
     } else if (qsDef.type === 'array') {
       if (qs.parent === undefined || ji.parent === undefined) {
         throw new Error('Internal Error, nested structure with no parent.');
diff --git a/test/src/databases/all/join.spec.ts b/test/src/databases/all/join.spec.ts
index 6ee64b89a8..791780f59d 100644
--- a/test/src/databases/all/join.spec.ts
+++ b/test/src/databases/all/join.spec.ts
@@ -24,6 +24,7 @@
 /* eslint-disable no-console */
 
 import {RuntimeList, allDatabases} from '../../runtimes';
+import {TestSelect} from '../../test-select';
 import {databasesFromEnvironmentOr} from '../../util';
 import '../../util/db-jest-matchers';
 
@@ -318,4 +319,66 @@ describe.each(runtimes.runtimeList)('%s', (databaseName, runtime) => {
       `).matchesRows(runtime, {pick_a1: [1]});
     }
   );
+  test('join ON expression references nested join dimension', async () => {
+    const ts = new TestSelect(runtime.dialect);
+    const usrSQL = ts.generate({id: 1, email: 'email@co.com'});
+    const resSQL = ts.generate({id: 1, user_id: 1});
+    const msgSQL = ts.generate({id: 1, msg_email: 'email@co.com'});
+    await expect(`
+      source: usr is ${databaseName}.sql("""${usrSQL}""")
+      source: res is ${databaseName}.sql("""${resSQL}""") extend {
+        join_one: usr on usr.id = user_id
+        dimension: usr_email is usr.email
+      }
+      source: msg is ${databaseName}.sql("""${msgSQL}""") extend {
+        join_many: res on res.usr_email = msg_email
+      }
+      run: msg -> {
+        group_by: msg_email, res.usr_email
+      }
+    `).malloyResultMatches(runtime, {
+      msg_email: 'email@co.com',
+      usr_email: 'email@co.com',
+    });
+  });
+  test('array field in joined source used in join condition', async () => {
+    const ts = new TestSelect(runtime.dialect);
+
+    // Mock GA4 events table with event_params array
+    const eventsSQL = ts.generate(
+      {
+        event_name: 'page_view',
+        event_params: [
+          {key: 'page_location', value: '/home'},
+          {key: 'page_title', value: 'Home Page'},
+        ],
+      },
+      {
+        event_name: 'user_engagement',
+        event_params: [
+          {key: 'engagement_time', value: '1000'},
+          {key: 'page_view', value: 'true'}, // This matches event_name from row 1
+        ],
+      },
+      {
+        event_name: 'scroll',
+        event_params: [{key: 'percent', value: '50'}],
+      }
+    );
+
+    await expect(`
+    source: ga4_1 is duckdb.sql("""${eventsSQL}""") extend {
+      dimension: event_param is event_params.key
+    }
+
+    source: ga4_2 is duckdb.sql("""${eventsSQL}""") extend {
+      join_one: ga4 is ga4_1 on event_name = ga4.event_param
+    }
+
+    run: ga4_2 -> {
+      aggregate: cnt is count()
+      where: ga4.event_param is not null
+    }
+  `).malloyResultMatches(runtime, {cnt: 1}); // Should match 'page_view' = 'page_view'
+  });
 });