diff --git a/payload_signer.cc b/payload_signer.cc
index 15c2b32..3d09737 100644
--- a/payload_signer.cc
+++ b/payload_signer.cc
@@ -230,6 +230,10 @@
   cmd[cmd.size() - 3] = hash_path;
   cmd[cmd.size() - 1] = sig_path;
 
+  // When running unittests, we need to use the openssl version from the
+  // SYSROOT instead of the one on the $PATH (host).
+  cmd[0] = utils::GetPathOnBoard("openssl");
+
   int return_code = 0;
   TEST_AND_RETURN_FALSE(Subprocess::SynchronousExec(cmd, &return_code, NULL));
   TEST_AND_RETURN_FALSE(return_code == 0);