diff --git a/AMSS_NCKU_source/bssnEScalar_class.C b/AMSS_NCKU_source/bssnEScalar_class.C
index 96cd5fe..cc29f44 100644
--- a/AMSS_NCKU_source/bssnEScalar_class.C
+++ b/AMSS_NCKU_source/bssnEScalar_class.C
@@ -1757,7 +1757,7 @@ void bssnEScalar_class::Step(int lev, int YN)
 #if USE_CUDA_BSSN
   {
     const char *mixed_env = getenv("AMSS_ESCALAR_MIXED_GPU_RP");
-    const bool mixed_gpu_rp = (!mixed_env || atoi(mixed_env) != 0);
+    const bool mixed_gpu_rp = (mixed_env && atoi(mixed_env) != 0);
     const char *split_env = getenv("AMSS_ESCALAR_SPLIT_RP");
     const bool split_rp = (split_env && atoi(split_env) != 0);
     if (!mixed_gpu_rp && !split_rp)
diff --git a/AMSS_NCKU_source/bssn_class.C b/AMSS_NCKU_source/bssn_class.C
index b891ad4..f3a5b26 100644
--- a/AMSS_NCKU_source/bssn_class.C
+++ b/AMSS_NCKU_source/bssn_class.C
@@ -108,7 +108,7 @@ int amss_escalar_mixed_gpu_rp_enabled()
   if (enabled < 0)
   {
     const char *env = getenv("AMSS_ESCALAR_MIXED_GPU_RP");
-    enabled = (!env || atoi(env) != 0) ? 1 : 0;
+    enabled = (env && atoi(env) != 0) ? 1 : 0;
   }
   return enabled;
 }