diff --git a/src/future/exec/ExecFuture.php b/src/future/exec/ExecFuture.php
--- a/src/future/exec/ExecFuture.php
+++ b/src/future/exec/ExecFuture.php
@@ -426,7 +426,10 @@
   public function resolveKill() {
     if (!$this->result) {
       $signal = 9;
-      proc_terminate($this->proc, $signal);
+
+      if ($this->proc) {
+        proc_terminate($this->proc, $signal);
+      }
 
       $this->result = array(
         128 + $signal,
diff --git a/src/future/exec/__tests__/ExecFutureTestCase.php b/src/future/exec/__tests__/ExecFutureTestCase.php
--- a/src/future/exec/__tests__/ExecFutureTestCase.php
+++ b/src/future/exec/__tests__/ExecFutureTestCase.php
@@ -63,6 +63,14 @@
     $future->resolve();
   }
 
+  public function testTerminateWithoutStart() {
+    // We never start this future, but it should be fine to kill a future from
+    // any state.
+    $future = new ExecFuture('sleep 1');
+    $future->resolveKill();
+
+    $this->assertTrue(true);
+  }
 
   public function testTimeoutTestShouldRunLessThan1Sec() {
     // NOTE: This is partly testing that we choose appropriate select wait