diff --git a/butane/tests/basic.rs b/butane/tests/basic.rs
index e69abe66..7304e9d7 100644
--- a/butane/tests/basic.rs
+++ b/butane/tests/basic.rs
@@ -401,3 +401,21 @@ fn basic_load_first_ordered(conn: Connection) {
     assert_eq!(found_desc, Some(foo2));
 }
 testall!(basic_load_first_ordered);
+
+fn save_upserts_by_default(conn: Connection) {
+    let mut foo = Foo::new(1);
+    foo.bar = 42;
+    foo.save(&conn).unwrap();
+
+    // Create another foo object with the same primary key,
+    // but a different bar value.
+    let mut foo = Foo::new(1);
+    foo.bar = 43;
+    // Save should do an upsert, so it will update the bar value
+    // rather than throwing a conflict
+    foo.save(&conn).unwrap();
+
+    let retrieved = Foo::get(&conn, 1).unwrap();
+    assert_eq!(retrieved.bar, 43);
+}
+testall!(save_upserts_by_default);
diff --git a/butane_core/src/codegen/dbobj.rs b/butane_core/src/codegen/dbobj.rs
index 2a8fd0e7..20ab7389 100644
--- a/butane_core/src/codegen/dbobj.rs
+++ b/butane_core/src/codegen/dbobj.rs
@@ -71,6 +71,7 @@ pub fn impl_dbobject(ast_struct: &ItemStruct, config: &Config) -> TokenStream2 {
                     #pklit,
                     <#pktype as butane::FieldType>::SQLTYPE);
                 if self.state.saved {
+                    // Already exists in db, do an update
                     #(#values_no_pk)*
                     if values.len() > 0 {
                         conn.update(Self::TABLE,
@@ -78,10 +79,17 @@ pub fn impl_dbobject(ast_struct: &ItemStruct, config: &Config) -> TokenStream2 {
                                     butane::ToSql::to_sql_ref(self.pk()),
                                     &[#save_cols], &values)?;
                     }
-                } else {
+                } else if #auto_pk {
+                    // Since we expect our pk field to be invalid and to be created by the insert,
+                    // we do a pure insert, no upsert allowed.
                     #(#values)*
                     let pk = conn.insert_returning_pk(Self::TABLE, &[#insert_cols], &pkcol, &values)?;
                     #(#post_insert)*
+                } else {
+                    // Do an upsert
+                    #(#values)*
+                    conn.insert_or_replace(Self::TABLE, &[#insert_cols], &pkcol, &values)?;
+                    self.state.saved = true
                 }
                 #many_save
                 Ok(())
diff --git a/butane_core/src/db/pg.rs b/butane_core/src/db/pg.rs
index c9f372a2..a0263202 100644
--- a/butane_core/src/db/pg.rs
+++ b/butane_core/src/db/pg.rs
@@ -715,14 +715,20 @@ pub fn sql_insert_or_replace_with_placeholders(
         n + 1
     });
     write!(w, ")").unwrap();
-    write!(w, " ON CONFLICT ({}) DO UPDATE SET (", pkcol.name()).unwrap();
-    helper::list_columns(columns, w);
-    write!(w, ") = (").unwrap();
-    columns.iter().fold("", |sep, c| {
-        write!(w, "{}excluded.{}", sep, c.name()).unwrap();
-        ", "
-    });
-    write!(w, ")").unwrap();
+    write!(w, " ON CONFLICT ({}) DO ", pkcol.name()).unwrap();
+    if columns.len() > 1 {
+        write!(w, "UPDATE SET (").unwrap();
+        helper::list_columns(columns, w);
+        write!(w, ") = (").unwrap();
+        columns.iter().fold("", |sep, c| {
+            write!(w, "{}excluded.{}", sep, c.name()).unwrap();
+            ", "
+        });
+        write!(w, ")").unwrap();
+    } else {
+        // If the pk is the only column and it already exists, then there's nothing to update.
+        write!(w, "NOTHING").unwrap();
+    }
 }
 
 fn pgtype_for_val(val: &SqlVal) -> postgres::types::Type {
diff --git a/butane_core/src/db/sqlite.rs b/butane_core/src/db/sqlite.rs
index 7640abb2..8be74455 100644
--- a/butane_core/src/db/sqlite.rs
+++ b/butane_core/src/db/sqlite.rs
@@ -198,11 +198,11 @@ impl ConnectionMethods for rusqlite::Connection {
         &self,
         table: &str,
         columns: &[Column],
-        _pkcol: &Column,
+        pkcol: &Column,
         values: &[SqlValRef],
     ) -> Result<()> {
         let mut sql = String::new();
-        sql_insert_or_update(table, columns, &mut sql);
+        sql_insert_or_update(table, columns, pkcol, &mut sql);
         self.execute(&sql, rusqlite::params_from_iter(values))?;
         Ok(())
     }
@@ -611,8 +611,8 @@ fn change_column(
     result
 }
 
-pub fn sql_insert_or_update(table: &str, columns: &[Column], w: &mut impl Write) {
-    write!(w, "INSERT OR REPLACE ").unwrap();
+pub fn sql_insert_or_update(table: &str, columns: &[Column], pkcol: &Column, w: &mut impl Write) {
+    write!(w, "INSERT ").unwrap();
     write!(w, "INTO {} (", helper::quote_reserved_word(table)).unwrap();
     helper::list_columns(columns, w);
     write!(w, ") VALUES (").unwrap();
@@ -621,6 +621,26 @@ pub fn sql_insert_or_update(table: &str, columns: &[Column], w: &mut impl Write)
         ", "
     });
     write!(w, ")").unwrap();
+    write!(w, " ON CONFLICT ({}) DO ", pkcol.name()).unwrap();
+    if columns.len() > 1 {
+        write!(w, "UPDATE SET (").unwrap();
+        helper::list_columns(columns, w);
+        write!(w, ") = (").unwrap();
+        columns.iter().fold("", |sep, c| {
+            write!(
+                w,
+                "{}excluded.{}",
+                sep,
+                helper::quote_reserved_word(c.name())
+            )
+            .unwrap();
+            ", "
+        });
+        write!(w, ")").unwrap();
+    } else {
+        // If the pk is the only column and it already exists, then there's nothing to update.
+        write!(w, "NOTHING").unwrap();
+    }
 }
 
 #[derive(Debug)]