diff --git a/src/Internal/PostgresHandleConnection.php b/src/Internal/PostgresHandleConnection.php
index 9a6cc57..edbe9e6 100644
--- a/src/Internal/PostgresHandleConnection.php
+++ b/src/Internal/PostgresHandleConnection.php
@@ -82,8 +82,10 @@ private function awaitPending(): void
      */
     private function reserve(): void
     {
+        $this->awaitPending();
         \assert($this->busy === null);
-        $this->busy = new DeferredFuture;
+
+        $this->busy = new DeferredFuture();
     }
 
     /**
diff --git a/test/AbstractConnectionTest.php b/test/AbstractConnectionTest.php
index b321835..67dd6aa 100644
--- a/test/AbstractConnectionTest.php
+++ b/test/AbstractConnectionTest.php
@@ -142,4 +142,21 @@ public function testTransactionsCallbacksOnDestruct(): void
         unset($transaction);
         delay(0.1); // Destructor is async, so give control to the loop to invoke callbacks.
     }
+
+    /**
+     * Ensure prior transaction has fully completed before attempting to begin another transaction.
+     * @see https://github.com/amphp/postgres/pull/73
+     */
+    public function testSequentialTransactionsWaitForPreviousRelease(): void
+    {
+        $connection = $this->executor;
+
+        $transaction = $connection->beginTransaction();
+        $transaction->onClose($this->createCallback(1));
+        $transaction->commit();
+
+        $transaction = $connection->beginTransaction();
+        $transaction->onClose($this->createCallback(1));
+        $transaction->commit();
+    }
 }