diff --git a/src/rt/memory_region.cpp b/src/rt/memory_region.cpp
index 29099fb14f27..e4130e80f5ac 100644
--- a/src/rt/memory_region.cpp
+++ b/src/rt/memory_region.cpp
@@ -204,14 +204,8 @@ memory_region::claim_alloc(void *mem) {
 
 void
 memory_region::maybe_poison(void *mem) {
-    // TODO: We should lock this, in case the compiler doesn't.
-    static int poison = -1;
-    if (poison < 0) {
-        char *env_str = getenv("RUST_POISON_ON_FREE");
-        poison = env_str != NULL && env_str[0] != '\0';
-    }
 
-    if (!poison)
+    if (!_srv->env->poison_on_free)
         return;
 
 #   if RUSTRT_TRACK_ALLOCATIONS >= 1
diff --git a/src/rt/rust_env.cpp b/src/rt/rust_env.cpp
index bdec4c284354..ab9bf9d75fa9 100644
--- a/src/rt/rust_env.cpp
+++ b/src/rt/rust_env.cpp
@@ -13,6 +13,7 @@
 #define CHECK_CLAIMS "CHECK_CLAIMS"
 #define DETAILED_LEAKS "DETAILED_LEAKS"
 #define RUST_SEED "RUST_SEED"
+#define RUST_POISON_ON_FREE "RUST_POISON_ON_FREE"
 
 #if defined(__WIN32__)
 static int
@@ -116,6 +117,7 @@ load_env() {
     env->check_claims = getenv(CHECK_CLAIMS) != NULL;
     env->detailed_leaks = getenv(DETAILED_LEAKS) != NULL;
     env->rust_seed = copyenv(RUST_SEED);
+    env->poison_on_free = getenv(RUST_POISON_ON_FREE) != NULL;
 
     return env;
 }
diff --git a/src/rt/rust_env.h b/src/rt/rust_env.h
index eecdb7931b4f..adf3dc8a7d48 100644
--- a/src/rt/rust_env.h
+++ b/src/rt/rust_env.h
@@ -6,6 +6,7 @@ struct rust_env {
     bool check_claims;
     bool detailed_leaks;
     char* rust_seed;
+    bool poison_on_free;
 };
 
 rust_env* load_env();