diff --git a/activerecord/lib/active_record/fixture_set/table_row.rb b/activerecord/lib/active_record/fixture_set/table_row.rb
index 6b4c7a935f..c96c0fed62 100644
--- a/activerecord/lib/active_record/fixture_set/table_row.rb
+++ b/activerecord/lib/active_record/fixture_set/table_row.rb
@@ -39,6 +39,29 @@ module ActiveRecord
         end
       end
 
+      class PrimaryKeyError < StandardError # :nodoc:
+        def initialize(label, association, value)
+          super(<<~MSG)
+            Unable to set #{association.name} to #{value} because the association has a
+            custom primary key (#{association.join_primary_key}) that does not match the
+            associated table's primary key (#{association.klass.primary_key}).
+
+            To fix this, change your fixture from
+
+            #{label}:
+              #{association.name}: #{value}
+
+            to
+
+            #{label}:
+              #{association.foreign_key}: **value**
+
+            where **value** is the #{association.join_primary_key} value for the
+            associated #{association.klass.name} record.
+          MSG
+        end
+      end
+
       def initialize(fixture, table_rows:, label:, now:)
         @table_rows = table_rows
         @label = label
@@ -119,9 +142,13 @@ module ActiveRecord
               fk_name = association.join_foreign_key
 
               if association.name.to_s != fk_name && value = @row.delete(association.name.to_s)
-                if association.polymorphic? && value.sub!(/\s*\(([^)]*)\)\s*$/, "")
-                  # support polymorphic belongs_to as "label (Type)"
-                  @row[association.join_foreign_type] = $1
+                if association.polymorphic?
+                  if value.sub!(/\s*\(([^)]*)\)\s*$/, "")
+                    # support polymorphic belongs_to as "label (Type)"
+                    @row[association.join_foreign_type] = $1
+                  end
+                elsif association.join_primary_key != association.klass.primary_key
+                  raise PrimaryKeyError.new(@label, association, value)
                 end
 
                 fk_type = reflection_class.type_for_attribute(fk_name).type
diff --git a/activerecord/test/cases/fixtures_test.rb b/activerecord/test/cases/fixtures_test.rb
index a466cccac9..dfd90c14ab 100644
--- a/activerecord/test/cases/fixtures_test.rb
+++ b/activerecord/test/cases/fixtures_test.rb
@@ -6,6 +6,7 @@ require "models/admin"
 require "models/admin/account"
 require "models/admin/randomly_named_c1"
 require "models/admin/user"
+require "models/author"
 require "models/binary"
 require "models/book"
 require "models/bulb"
@@ -18,6 +19,7 @@ require "models/course"
 require "models/developer"
 require "models/dog"
 require "models/doubloon"
+require "models/essay"
 require "models/joke"
 require "models/matey"
 require "models/other_dog"
@@ -1492,6 +1494,16 @@ class FileFixtureConflictTest < ActiveRecord::TestCase
   end
 end
 
+class PrimaryKeyErrorTest < ActiveRecord::TestCase
+  test "generates the correct value" do
+    e = assert_raise(ActiveRecord::FixtureSet::TableRow::PrimaryKeyError) do
+      ActiveRecord::FixtureSet.create_fixtures(FIXTURES_ROOT + "/primary_key_error", "primary_key_error")
+    end
+
+    assert_includes e.message, "Unable to set"
+  end
+end
+
 if current_adapter?(:SQLite3Adapter) && !in_memory_db?
   class MultipleFixtureConnectionsTest < ActiveRecord::TestCase
     include ActiveRecord::TestFixtures
diff --git a/activerecord/test/fixtures/primary_key_error/primary_key_error.yml b/activerecord/test/fixtures/primary_key_error/primary_key_error.yml
new file mode 100644
index 0000000000..b5edcec4ac
--- /dev/null
+++ b/activerecord/test/fixtures/primary_key_error/primary_key_error.yml
@@ -0,0 +1,6 @@
+_fixture:
+  model_class: Author
+
+david:
+  name: David
+  owned_essay: a_modest_proposal