diff --git a/commands/add/index.js b/commands/add/index.js
index 20c883e35f..e681724e37 100644
--- a/commands/add/index.js
+++ b/commands/add/index.js
@@ -147,7 +147,10 @@ class AddCommand extends Command {
     if (this.selfSatisfied) {
       const node = this.packageGraph.get(name);
 
-      return Promise.resolve(this.spec.saveRelativeFileSpec ? node.location : node.version);
+      // ALWAYS use POSIX path for relative file: specifiers
+      return Promise.resolve(
+        this.spec.saveRelativeFileSpec ? path.posix.normalize(node.location) : node.version
+      );
     }
 
     return packageJson(name, { version: fetchSpec }).then(pkg => pkg.version);
diff --git a/commands/add/lib/get-range-to-reference.js b/commands/add/lib/get-range-to-reference.js
index cf1398dbaf..9a65fe4474 100644
--- a/commands/add/lib/get-range-to-reference.js
+++ b/commands/add/lib/get-range-to-reference.js
@@ -11,8 +11,13 @@ function getRangeToReference(spec, deps, loc, prefix) {
   const resolved = spec.type === "tag" ? `${prefix}${spec.version}` : spec.fetchSpec;
 
   if (spec.saveRelativeFileSpec) {
-    // "version" has been resolved to pkg.location in getPackageVersion()
-    return npa.resolve(spec.name, path.relative(loc, spec.version), loc).saveSpec;
+    // ALWAYS render a POSIX file: spec, Windows can deal with it
+    const where = path.posix.normalize(loc);
+
+    // "spec.version" has been resolved to pkg.location in getPackageVersion()
+    const relativeFileSpec = `file:${path.posix.relative(where, spec.version)}`;
+
+    return npa.resolve(spec.name, relativeFileSpec, where).saveSpec;
   }
 
   if (prefix && current && semver.intersects(current, resolved)) {