diff --git a/db-service/lib/cqn4sql.js b/db-service/lib/cqn4sql.js
index 96c32fb59..cb5f71282 100644
--- a/db-service/lib/cqn4sql.js
+++ b/db-service/lib/cqn4sql.js
@@ -1827,7 +1827,6 @@ function cqn4sql(originalQuery, model) {
     const { on, keys } = assocRefLink.definition
     const target = getDefinition(assocRefLink.definition.target)
     let res
-    // technically we could have multiple backlinks
     if (keys) {
       const fkPkPairs = getParentKeyForeignKeyPairs(assocRefLink.definition, targetSideRefLink, true)
       const transformedOn = []
@@ -1960,6 +1959,12 @@ function cqn4sql(originalQuery, model) {
               }
             })
           } else if (backlink.keys) {
+            // sanity check: error out if we can't produce a join
+            if (backlink.keys.length === 0) {
+              throw new Error(
+                `Path step “${assocRefLink.alias}” is a self comparison with “${getFullName(backlink)}” that has no foreign keys`,
+              )
+            }
             // managed backlink -> calculate fk-pk pairs
             const fkPkPairs = getParentKeyForeignKeyPairs(backlink, targetSideRefLink)
             fkPkPairs.forEach((pair, j) => {
diff --git a/db-service/test/cqn4sql/keyless.test.js b/db-service/test/cqn4sql/keyless.test.js
index 258c4d632..b55c2345f 100644
--- a/db-service/test/cqn4sql/keyless.test.js
+++ b/db-service/test/cqn4sql/keyless.test.js
@@ -12,61 +12,96 @@ describe('keyless entities', () => {
   beforeAll(async () => {
     model = await cds.load(__dirname + '/model/keyless').then(cds.linked)
   })
-
-  it('no foreign keys for join', () => {
-    const { Books } = model.entities
-    const q = SELECT.from(Books).where(`author[ID = 42].book[ID = 42].author.name LIKE 'King'`)
-    expect(() => cqn4sql(q, model)).to.throw(
-      'Path step “author” of “author[…].book[…].author.name” has no foreign keys',
-    )
-    // ok if explicit foreign key is used
-    const qOk = SELECT.columns('ID').from(Books).where(`authorWithExplicitForeignKey[ID = 42].name LIKE 'King'`)
-    expect(cqn4sql(qOk, model)).to.eql(
-      CQL`SELECT Books.ID FROM Books as Books 
+  describe('managed assocs', () => {
+    it('no foreign keys for join', () => {
+      const { Books } = model.entities
+      const q = SELECT.from(Books).where(`author[ID = 42].book[ID = 42].author.name LIKE 'King'`)
+      expect(() => cqn4sql(q, model)).to.throw(
+        'Path step “author” of “author[…].book[…].author.name” has no foreign keys',
+      )
+      // ok if explicit foreign key is used
+      const qOk = SELECT.columns('ID').from(Books).where(`authorWithExplicitForeignKey[ID = 42].name LIKE 'King'`)
+      expect(cqn4sql(qOk, model)).to.eql(
+        CQL`SELECT Books.ID FROM Books as Books 
         left join Authors as authorWithExplicitForeignKey
           on authorWithExplicitForeignKey.ID = Books.authorWithExplicitForeignKey_ID
           and authorWithExplicitForeignKey.ID = 42
         where authorWithExplicitForeignKey.name LIKE 'King'`,
-    )
-  })
-  it('scoped query leading to where exists subquery cant be constructed', () => {
-    const q = SELECT.from('Books:author')
-    expect(() => cqn4sql(q, model)).to.throw(`Path step “author” of “Books:author” has no foreign keys`)
+      )
+    })
+    it('no foreign keys for join (2)', () => {
+      const { Authors } = model.entities
+      const q = SELECT.from(Authors).where(`book.authorWithExplicitForeignKey.book.my.author LIKE 'King'`)
+      expect(() => cqn4sql(q, model)).to.throw(
+        'Path step “author” of “book.authorWithExplicitForeignKey.book.my.author” has no foreign keys',
+      )
+    })
+    it('scoped query leading to where exists subquery cant be constructed', () => {
+      const q = SELECT.from('Books:author')
+      expect(() => cqn4sql(q, model)).to.throw(`Path step “author” of “Books:author” has no foreign keys`)
 
-    // ok if explicit foreign key is used
-    const qOk = SELECT.from('Books:authorWithExplicitForeignKey').columns('ID')
-    expect(cqn4sql(qOk, model)).to.eql(
-      CQL`SELECT authorWithExplicitForeignKey.ID FROM Authors as authorWithExplicitForeignKey 
+      // ok if explicit foreign key is used
+      const qOk = SELECT.from('Books:authorWithExplicitForeignKey').columns('ID')
+      expect(cqn4sql(qOk, model)).to.eql(
+        CQL`SELECT authorWithExplicitForeignKey.ID FROM Authors as authorWithExplicitForeignKey 
         where exists (
           SELECT 1 from Books as Books where Books.authorWithExplicitForeignKey_ID = authorWithExplicitForeignKey.ID
         )`,
-    )
-  })
-  it('where exists predicate cant be transformed to subquery', () => {
-    const q = SELECT.from('Books').where('exists author')
-    expect(() => cqn4sql(q, model)).to.throw(`Path step “author” of “author” has no foreign keys`)
-    // ok if explicit foreign key is used
-    const qOk = SELECT.from('Books').columns('ID').where('exists authorWithExplicitForeignKey')
-    expect(cqn4sql(qOk, model)).to.eql(
-      CQL`SELECT Books.ID FROM Books as Books 
+      )
+    })
+    it('where exists predicate cant be transformed to subquery', () => {
+      const q = SELECT.from('Books').where('exists author')
+      expect(() => cqn4sql(q, model)).to.throw(`Path step “author” of “author” has no foreign keys`)
+      // ok if explicit foreign key is used
+      const qOk = SELECT.from('Books').columns('ID').where('exists authorWithExplicitForeignKey')
+      expect(cqn4sql(qOk, model)).to.eql(
+        CQL`SELECT Books.ID FROM Books as Books 
         where exists (
           SELECT 1 from Authors as authorWithExplicitForeignKey where authorWithExplicitForeignKey.ID = Books.authorWithExplicitForeignKey_ID
         )`,
-    )
-  })
-  it('correlated subquery for expand cant be constructed', () => {
-    const q = CQL`SELECT author { name } from Books`
-    expect(() => cqn4sql(q, model)).to.throw(`Can't expand “author” as it has no foreign keys`)
-    // ok if explicit foreign key is used
-    const qOk = CQL`SELECT authorWithExplicitForeignKey { name } from Books`
-    expect(JSON.parse(JSON.stringify(cqn4sql(qOk, model)))).to.eql(
-      CQL`
+      )
+    })
+    it('correlated subquery for expand cant be constructed', () => {
+      const q = CQL`SELECT author { name } from Books`
+      expect(() => cqn4sql(q, model)).to.throw(`Can't expand “author” as it has no foreign keys`)
+      // ok if explicit foreign key is used
+      const qOk = CQL`SELECT authorWithExplicitForeignKey { name } from Books`
+      expect(JSON.parse(JSON.stringify(cqn4sql(qOk, model)))).to.eql(
+        CQL`
       SELECT
         (
           SELECT authorWithExplicitForeignKey.name from Authors as authorWithExplicitForeignKey
           where Books.authorWithExplicitForeignKey_ID = authorWithExplicitForeignKey.ID
         ) as authorWithExplicitForeignKey
       from Books as Books`,
-    )
+      )
+    })
+  })
+  describe('managed assocs as backlinks', () => {
+    it('backlink has no foreign keys for join', () => {
+      const { Authors } = model.entities
+      const q = SELECT.from(Authors).where(`bookWithBackLink.title LIKE 'Potter'`)
+      expect(() => cqn4sql(q, model)).to.throw(
+        `Path step “bookWithBackLink” is a self comparison with “author” that has no foreign keys`,
+      )
+    })
+    it('backlink has no foreign keys for scoped query', () => {
+      const q = SELECT.from('Authors:bookWithBackLink')
+      expect(() => cqn4sql(q, model)).to.throw(
+        `Path step “bookWithBackLink” is a self comparison with “author” that has no foreign keys`,
+      )
+    })
+    it('backlink has no foreign keys for where exists subquery', () => {
+      const q = SELECT.from('Authors').where('exists bookWithBackLink')
+      expect(() => cqn4sql(q, model)).to.throw(
+        `Path step “bookWithBackLink” is a self comparison with “author” that has no foreign keys`,
+      )
+    })
+    it('backlink has no foreign keys for expand subquery', () => {
+      const q = CQL`SELECT bookWithBackLink { title } from Authors`
+      expect(() => cqn4sql(q, model)).to.throw(
+        `Path step “bookWithBackLink” is a self comparison with “author” that has no foreign keys`,
+      )
+    })
   })
 })
diff --git a/db-service/test/cqn4sql/model/keyless.cds b/db-service/test/cqn4sql/model/keyless.cds
index 815413259..efb756ca0 100644
--- a/db-service/test/cqn4sql/model/keyless.cds
+++ b/db-service/test/cqn4sql/model/keyless.cds
@@ -12,4 +12,6 @@ entity Authors {
   ID : Integer;
   name   : String;
   book: Association to Books;
+  // backlink has no foreign keys...
+  bookWithBackLink: Association to Books on bookWithBackLink.author = $self;
 }