diff --git a/src/librustc_trans/trans/context.rs b/src/librustc_trans/trans/context.rs
index f2de949ccd53..42e2efa90625 100644
--- a/src/librustc_trans/trans/context.rs
+++ b/src/librustc_trans/trans/context.rs
@@ -933,11 +933,33 @@ fn declare_intrinsic(ccx: &CrateContext, key: & &'static str) -> Option<ValueRef
     ifn!("llvm.lifetime.end", fn(t_i64, i8p) -> void);
 
     ifn!("llvm.expect.i1", fn(i1, i1) -> i1);
-    ifn!("llvm.assume", fn(i1) -> void);
 
     // Some intrinsics were introduced in later versions of LLVM, but they have
     // fallbacks in libc or libm and such.
     macro_rules! compatible_ifn {
+        ($name:expr, noop($cname:ident ($($arg:expr),*) -> void), $llvm_version:expr) => (
+            if unsafe { llvm::LLVMVersionMinor() >= $llvm_version } {
+                // The `if key == $name` is already in ifn!
+                ifn!($name, fn($($arg),*) -> void);
+            } else if *key == $name {
+                let f = declare::declare_cfn(ccx, stringify!($cname),
+                                             Type::func(&[$($arg),*], &void),
+                                             ty::mk_nil(ccx.tcx()));
+                llvm::SetLinkage(f, llvm::InternalLinkage);
+
+                let bld = ccx.builder();
+                let llbb = unsafe {
+                    llvm::LLVMAppendBasicBlockInContext(ccx.llcx(), f,
+                                                        "entry-block\0".as_ptr() as *const _)
+                };
+
+                bld.position_at_end(llbb);
+                bld.ret_void();
+
+                ccx.intrinsics().borrow_mut().insert($name, f.clone());
+                return Some(f);
+            }
+        );
         ($name:expr, $cname:ident ($($arg:expr),*) -> $ret:expr, $llvm_version:expr) => (
             if unsafe { llvm::LLVMVersionMinor() >= $llvm_version } {
                 // The `if key == $name` is already in ifn!
@@ -952,6 +974,8 @@ fn declare_intrinsic(ccx: &CrateContext, key: & &'static str) -> Option<ValueRef
         )
     }
 
+    compatible_ifn!("llvm.assume", noop(llvmcompat_assume(i1) -> void), 6);
+
     if ccx.sess().opts.debuginfo != NoDebugInfo {
         ifn!("llvm.dbg.declare", fn(Type::metadata(ccx), Type::metadata(ccx)) -> void);
         ifn!("llvm.dbg.value", fn(Type::metadata(ccx), t_i64, Type::metadata(ccx)) -> void);