diff --git a/packages/react-dom-bindings/src/server/ReactDOMServerExternalRuntime.js b/packages/react-dom-bindings/src/server/ReactDOMServerExternalRuntime.js
index 63f5b64d93c8c..bc9e0ccb32624 100644
--- a/packages/react-dom-bindings/src/server/ReactDOMServerExternalRuntime.js
+++ b/packages/react-dom-bindings/src/server/ReactDOMServerExternalRuntime.js
@@ -9,17 +9,12 @@
 // and by rollup in jest unit tests
 import {
   clientRenderBoundary,
-  completeBoundaryWithStyles,
+  completeBoundaryWithStylesInlineLocals,
   completeBoundary,
   completeSegment,
 } from './fizz-instruction-set/ReactDOMFizzInstructionSet';
 
-if (!window.$RC) {
-  // TODO: Eventually remove, we currently need to set these globals for
-  // compatibility with ReactDOMFizzInstructionSet
-  window.$RC = completeBoundary;
-  window.$RM = new Map();
-}
+const resourceMap = new Map();
 
 if (document.readyState === 'loading') {
   if (document.body != null) {
@@ -91,7 +86,8 @@ function handleNode(node_ /*: Node */) {
     node.remove();
   } else if (dataset['rri'] != null) {
     // Convert styles here, since its type is Array<Array<string>>
-    completeBoundaryWithStyles(
+    completeBoundaryWithStylesInlineLocals(
+      resourceMap,
       dataset['bid'],
       dataset['sid'],
       JSON.parse(dataset['sty']),
diff --git a/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInlineCompleteBoundaryWithStyles.js b/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInlineCompleteBoundaryWithStyles.js
index 62760ee543b5d..0d07636b63772 100644
--- a/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInlineCompleteBoundaryWithStyles.js
+++ b/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInlineCompleteBoundaryWithStyles.js
@@ -1,7 +1,7 @@
-import {completeBoundaryWithStyles} from './ReactDOMFizzInstructionSet';
+import {completeBoundaryWithStylesInlineGlobals} from './ReactDOMFizzInstructionSet';
 
 // This is a string so Closure's advanced compilation mode doesn't mangle it.
 // eslint-disable-next-line dot-notation
 window['$RM'] = new Map();
 // eslint-disable-next-line dot-notation
-window['$RR'] = completeBoundaryWithStyles;
+window['$RR'] = completeBoundaryWithStylesInlineGlobals;
diff --git a/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInstructionSet.js b/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInstructionSet.js
index 4abe722309f74..eea5c457b4efb 100644
--- a/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInstructionSet.js
+++ b/packages/react-dom-bindings/src/server/fizz-instruction-set/ReactDOMFizzInstructionSet.js
@@ -42,16 +42,121 @@ export function clientRenderBoundary(
   }
 }
 
-export function completeBoundaryWithStyles(
+// The following two functions should be almost identical. The only differences
+//  are the values used for `completeBoundaryImpl` and `resourceMap`.
+// completeBoundaryWithStylesInlineLocals is used by the Fizz external runtime, which
+//  bundles together all Fizz instruction functions (and is able to reference / rename
+//  completeBoundary and resourceMap as locals).
+// completeBoundaryWithStylesInlineGlobals is used by the Fizz inline script writer,
+//  which sends Fizz instruction functions on an as-needed basis. This version needs
+//  to reference completeBoundary($RC) and resourceMap($RM) as globals.
+//
+// Ideally, Closure would take care of inlining a shared implementation, but I couldn't
+//  figure out a zero-overhead inline due to lack of a @inline compiler directive.
+export function completeBoundaryWithStylesInlineLocals(
+  resourceMap,
+  suspenseBoundaryID,
+  contentID,
+  styles,
+) {
+  const completeBoundaryImpl = completeBoundary;
+  const precedences = new Map();
+  const thisDocument = document;
+  let lastResource, node;
+
+  // Seed the precedence list with existing resources
+  const nodes = thisDocument.querySelectorAll(
+    'link[data-precedence],style[data-precedence]',
+  );
+  for (let i = 0; (node = nodes[i++]); ) {
+    precedences.set(node.dataset['precedence'], (lastResource = node));
+  }
+
+  let i = 0;
+  const dependencies = [];
+  let style, href, precedence, attr, loadingState, resourceEl;
+
+  function setStatus(s) {
+    this['s'] = s;
+  }
+
+  while ((style = styles[i++])) {
+    let j = 0;
+    href = style[j++];
+    // We check if this resource is already in our resourceMap and reuse it if so.
+    // If it is already loaded we don't return it as a depenendency since there is nothing
+    // to wait for
+    loadingState = resourceMap.get(href);
+    if (loadingState) {
+      if (loadingState['s'] !== 'l') {
+        dependencies.push(loadingState);
+      }
+      continue;
+    }
+
+    // We construct our new resource element, looping over remaining attributes if any
+    // setting them to the Element.
+    resourceEl = thisDocument.createElement('link');
+    resourceEl.href = href;
+    resourceEl.rel = 'stylesheet';
+    resourceEl.dataset['precedence'] = precedence = style[j++];
+    while ((attr = style[j++])) {
+      resourceEl.setAttribute(attr, style[j++]);
+    }
+
+    // We stash a pending promise in our map by href which will resolve or reject
+    // when the underlying resource loads or errors. We add it to the dependencies
+    // array to be returned.
+    loadingState = resourceEl['_p'] = new Promise((re, rj) => {
+      resourceEl.onload = re;
+      resourceEl.onerror = rj;
+    });
+    loadingState.then(
+      setStatus.bind(loadingState, LOADED),
+      setStatus.bind(loadingState, ERRORED),
+    );
+    resourceMap.set(href, loadingState);
+    dependencies.push(loadingState);
+
+    // The prior style resource is the last one placed at a given
+    // precedence or the last resource itself which may be null.
+    // We grab this value and then update the last resource for this
+    // precedence to be the inserted element, updating the lastResource
+    // pointer if needed.
+    const prior = precedences.get(precedence) || lastResource;
+    if (prior === lastResource) {
+      lastResource = resourceEl;
+    }
+    precedences.set(precedence, resourceEl);
+
+    // Finally, we insert the newly constructed instance at an appropriate location
+    // in the Document.
+    if (prior) {
+      prior.parentNode.insertBefore(resourceEl, prior.nextSibling);
+    } else {
+      const head = thisDocument.head;
+      head.insertBefore(resourceEl, head.firstChild);
+    }
+  }
+
+  Promise.all(dependencies).then(
+    completeBoundaryImpl.bind(null, suspenseBoundaryID, contentID, ''),
+    completeBoundaryImpl.bind(
+      null,
+      suspenseBoundaryID,
+      contentID,
+      'Resource failed to load',
+    ),
+  );
+}
+
+export function completeBoundaryWithStylesInlineGlobals(
   suspenseBoundaryID,
   contentID,
   styles,
 ) {
-  // TODO: In the non-inline version of the runtime, these don't need to be read
-  // from the global scope.
   const completeBoundaryImpl = window['$RC'];
   const resourceMap = window['$RM'];
-
   const precedences = new Map();
   const thisDocument = document;
   let lastResource, node;