diff --git a/library/std/src/sys/windows/c.rs b/library/std/src/sys/windows/c.rs
index 0906edb0d85e3..2eb95b4bed9e8 100644
--- a/library/std/src/sys/windows/c.rs
+++ b/library/std/src/sys/windows/c.rs
@@ -551,6 +551,18 @@ compat_fn_with_fallback! {
         SetLastError(ERROR_CALL_NOT_IMPLEMENTED as DWORD);
         FALSE
     }
+
+    // >= Vista / Server 2008
+    // https://docs.microsoft.com/en-us/windows/win32/api/stringapiset/nf-stringapiset-comparestringordinal
+    pub fn CompareStringOrdinal(
+        lpString1: PCWSTR,
+        cchCount1: i32,
+        lpString2: PCWSTR,
+        cchCount2: i32,
+        bIgnoreCase: BOOL
+    ) -> COMPARESTRING_RESULT {
+        rtabort!("unavailable")
+    }
 }
 
 compat_fn_optional! {
diff --git a/library/std/src/sys/windows/c/windows_sys.lst b/library/std/src/sys/windows/c/windows_sys.lst
index 7e83e7143fcc6..97579d0c7748b 100644
--- a/library/std/src/sys/windows/c/windows_sys.lst
+++ b/library/std/src/sys/windows/c/windows_sys.lst
@@ -1941,7 +1941,6 @@ Windows.Win32.Foundation.WAIT_OBJECT_0
 Windows.Win32.Foundation.WAIT_TIMEOUT
 Windows.Win32.Foundation.WIN32_ERROR
 Windows.Win32.Globalization.COMPARESTRING_RESULT
-Windows.Win32.Globalization.CompareStringOrdinal
 Windows.Win32.Globalization.CP_UTF8
 Windows.Win32.Globalization.CSTR_EQUAL
 Windows.Win32.Globalization.CSTR_GREATER_THAN
diff --git a/library/std/src/sys/windows/c/windows_sys.rs b/library/std/src/sys/windows/c/windows_sys.rs
index 7b07fe3467cdb..3bacae1c9714b 100644
--- a/library/std/src/sys/windows/c/windows_sys.rs
+++ b/library/std/src/sys/windows/c/windows_sys.rs
@@ -16,16 +16,6 @@ extern "system" {
     pub fn CloseHandle(hobject: HANDLE) -> BOOL;
 }
 #[link(name = "kernel32")]
-extern "system" {
-    pub fn CompareStringOrdinal(
-        lpstring1: PCWSTR,
-        cchcount1: i32,
-        lpstring2: PCWSTR,
-        cchcount2: i32,
-        bignorecase: BOOL,
-    ) -> COMPARESTRING_RESULT;
-}
-#[link(name = "kernel32")]
 extern "system" {
     pub fn CreateDirectoryW(
         lppathname: PCWSTR,
diff --git a/library/std/src/sys/windows/process.rs b/library/std/src/sys/windows/process.rs
index e8f82c8f44587..63b0cc646f3b1 100644
--- a/library/std/src/sys/windows/process.rs
+++ b/library/std/src/sys/windows/process.rs
@@ -74,6 +74,10 @@ impl EnvKey {
 // [4] https://docs.microsoft.com/en-us/windows/win32/api/stringapiset/nf-stringapiset-comparestringordinal
 impl Ord for EnvKey {
     fn cmp(&self, other: &Self) -> cmp::Ordering {
+        if !c::CompareStringOrdinal::available() {
+            return self.os_string.cmp(&other.os_string);
+        }
+
         unsafe {
             let result = c::CompareStringOrdinal(
                 self.utf16.as_ptr(),
@@ -99,6 +103,10 @@ impl PartialOrd for EnvKey {
 }
 impl PartialEq for EnvKey {
     fn eq(&self, other: &Self) -> bool {
+        if !c::CompareStringOrdinal::available() {
+            return self.os_string == other.os_string;
+        }
+
         if self.utf16.len() != other.utf16.len() {
             false
         } else {
@@ -124,7 +132,12 @@ impl PartialEq<str> for EnvKey {
 // Environment variable keys should preserve their original case even though
 // they are compared using a caseless string mapping.
 impl From<OsString> for EnvKey {
-    fn from(k: OsString) -> Self {
+    fn from(mut k: OsString) -> Self {
+        if !c::CompareStringOrdinal::available() {
+            k.make_ascii_uppercase();
+            return EnvKey { utf16: Vec::new(), os_string: k };
+        }
+
         EnvKey { utf16: k.encode_wide().collect(), os_string: k }
     }
 }
@@ -818,8 +831,12 @@ fn make_envp(maybe_env: Option<BTreeMap<EnvKey, OsString>>) -> io::Result<(*mut
         }
 
         for (k, v) in env {
-            ensure_no_nuls(k.os_string)?;
-            blk.extend(k.utf16);
+            if !c::CompareStringOrdinal::available() {
+                blk.extend(ensure_no_nuls(k.os_string)?.encode_wide());
+            } else {
+                ensure_no_nuls(k.os_string)?;
+                blk.extend(k.utf16);
+            }
             blk.push('=' as u16);
             blk.extend(ensure_no_nuls(v)?.encode_wide());
             blk.push(0);