diff --git a/activerecord/lib/active_record/relation.rb b/activerecord/lib/active_record/relation.rb
index 58f7b74198cf5..3b22be78cbdb0 100644
--- a/activerecord/lib/active_record/relation.rb
+++ b/activerecord/lib/active_record/relation.rb
@@ -319,8 +319,13 @@ def to_sql
     end
 
     def where_values_hash
-      Hash[@where_values.find_all {|w| w.respond_to?(:operator) && w.operator == :== }.map {|where|
-        [where.operand1.name, where.operand2.respond_to?(:value) ? where.operand2.value : where.operand2]
+      Hash[@where_values.find_all { |w|
+        w.respond_to?(:operator) && w.operator == :== && w.left.relation.name == table_name
+      }.map { |where|
+        [
+          where.left.name,
+          where.right.respond_to?(:value) ? where.right.value : where.right
+        ]
       }]
     end
 
diff --git a/activerecord/lib/active_record/relation/spawn_methods.rb b/activerecord/lib/active_record/relation/spawn_methods.rb
index d761bd3ea604a..a61a3bd41c5d8 100644
--- a/activerecord/lib/active_record/relation/spawn_methods.rb
+++ b/activerecord/lib/active_record/relation/spawn_methods.rb
@@ -30,13 +30,14 @@ def merge(r)
 
       unless @where_values.empty?
         # Remove duplicates, last one wins.
-        seen = {}
+        seen = Hash.new { |h,table| h[table] = {} }
         merged_wheres = merged_wheres.reverse.reject { |w|
           nuke = false
           if w.respond_to?(:operator) && w.operator == :==
-            name       = w.left.name
-            nuke       = seen[name]
-            seen[name] = true
+            name              = w.left.name
+            table             = w.left.relation.name
+            nuke              = seen[table][name]
+            seen[table][name] = true
           end
           nuke
         }.reverse