diff --git a/src/fastalloc/mod.rs b/src/fastalloc/mod.rs
index 17699db2..60e19f89 100644
--- a/src/fastalloc/mod.rs
+++ b/src/fastalloc/mod.rs
@@ -1135,6 +1135,9 @@ impl<'a, F: Function> Env<'a, F> {
 
     fn alloc_inst(&mut self, block: Block, inst: Inst) -> Result<(), RegAllocError> {
         trace!("Allocating instruction {:?}", inst);
+        if self.func.requires_refs_on_stack(inst) {
+            panic!("Safepoint instructions aren't supported");
+        }
         if self.func.is_branch(inst) {
             self.process_branch(block, inst);
         }
diff --git a/src/fastalloc/vregset.rs b/src/fastalloc/vregset.rs
index 0eaa2d79..8f261eb0 100644
--- a/src/fastalloc/vregset.rs
+++ b/src/fastalloc/vregset.rs
@@ -1,7 +1,7 @@
 use alloc::vec::Vec;
 use alloc::vec;
 use core::fmt;
-use std::convert::{TryFrom, TryInto};
+use core::convert::{TryFrom, TryInto};
 use crate::{RegClass, VReg};
 
 struct RegClassNum;