diff --git a/src/comp/back/x86.rs b/src/comp/back/x86.rs
index d4b76352ca2..86631e93bf1 100644
--- a/src/comp/back/x86.rs
+++ b/src/comp/back/x86.rs
@@ -2,6 +2,7 @@ import lib.llvm.llvm;
 import lib.llvm.llvm.ModuleRef;
 import std._str;
 import std._vec;
+import std.os.target_os;
 import util.common.istr;
 
 const int wordsz = 4;
@@ -128,7 +129,11 @@ fn decl_upcall_glue(int align, str prefix, uint n) -> str {
 
 fn get_module_asm() -> str {
     auto align = 4;
+
     auto prefix = "";
+    if (target_os() == "macos") {
+        prefix = "_";
+    }
 
     auto glues =
         vec(decl_glue(align, prefix,
diff --git a/src/lib/linux_os.rs b/src/lib/linux_os.rs
index ce2c0f79aea..d5ef2a6b800 100644
--- a/src/lib/linux_os.rs
+++ b/src/lib/linux_os.rs
@@ -47,6 +47,9 @@ fn exec_suffix() -> str {
     ret "";
 }
 
+fn target_os() -> str {
+    ret "linux";
+}
 
 // Local Variables:
 // mode: rust;
diff --git a/src/lib/macos_os.rs b/src/lib/macos_os.rs
index 1d96a2339b9..53a66b56bec 100644
--- a/src/lib/macos_os.rs
+++ b/src/lib/macos_os.rs
@@ -47,6 +47,10 @@ fn exec_suffix() -> str {
     ret "";
 }
 
+fn target_os() -> str {
+    ret "macos";
+}
+
 // Local Variables:
 // mode: rust;
 // fill-column: 78;
diff --git a/src/lib/win32_os.rs b/src/lib/win32_os.rs
index 6e1b9a9c8b1..9f9ec2c2b9e 100644
--- a/src/lib/win32_os.rs
+++ b/src/lib/win32_os.rs
@@ -38,6 +38,10 @@ fn exec_suffix() -> str {
     ret ".exe";
 }
 
+fn target_os() -> str {
+    ret "win32";
+}
+
 // Local Variables:
 // mode: rust;
 // fill-column: 78;