diff --git a/src/test/ui/env-vars.rs b/src/test/ui/env-vars.rs
index f73902c40066d..f5035bb2c6985 100644
--- a/src/test/ui/env-vars.rs
+++ b/src/test/ui/env-vars.rs
@@ -5,6 +5,14 @@ use std::env::*;
 
 fn main() {
     for (k, v) in vars_os() {
+        // On Windows, the environment variable NUMBER_OF_PROCESSORS has special meaning.
+        // Unfortunately, you can get different answers, depending on whether you are
+        // enumerating all environment variables or querying a specific variable.
+        // This was causing this test to fail on machines with more than 64 processors.
+        if cfg!(target_os = "windows") && k == "NUMBER_OF_PROCESSORS" {
+            continue;
+        }
+
         let v2 = var_os(&k);
         assert!(v2.as_ref().map(|s| &**s) == Some(&*v),
                 "bad vars->var transition: {:?} {:?} {:?}", k, v, v2);