diff --git a/NanoXLSX.Reader/Internal/Readers/DiscoveryReader.cs b/NanoXLSX.Reader/Internal/Readers/DiscoveryReader.cs
index 7cbe62e73..8221afed6 100644
--- a/NanoXLSX.Reader/Internal/Readers/DiscoveryReader.cs
+++ b/NanoXLSX.Reader/Internal/Readers/DiscoveryReader.cs
@@ -1,4 +1,4 @@
-/*
+/*
  * NanoXLSX is a small .NET library to generate and read XLSX (Microsoft Excel 2007 or newer) files in an easy and native way
  * Copyright Raphael Stoeckli © 2026
  * This library is licensed under the MIT License.
@@ -238,10 +238,23 @@ private RelationshipInfo ParseRelationship(XmlReader reader, string relationship
             string resolvedTargetPath = null;
             if (targetMode == TargetMode.Internal)
             {
-                if (targetUri.IsAbsoluteUri)
+                // [VENDOR-PATCH NanoXLSX#mono-rootrelative-target] A target beginning with '/' is a
+                // ROOT-RELATIVE path, which OPC permits for an internal relationship. Mono's System.Uri
+                // parses such a string as an ABSOLUTE Uri while .NET's does not, so testing IsAbsoluteUri
+                // alone silently discards every root-relative relationship on Mono. In practice that is
+                // sharedStrings.xml: the relationship is dropped from the catalog, the (optional) shared
+                // strings part is never read, and every string cell is left holding its raw shared-string
+                // INDEX instead of its text -- with no exception raised. Test for a real scheme instead,
+                // and rebuild the target as relative so ResolvePartUri agrees on both runtimes.
+                bool rootRelativeTarget = target.StartsWith("/", StringComparison.Ordinal);
+                if (targetUri.IsAbsoluteUri && !rootRelativeTarget)
                 {
                     return HandleRelationshipIssue(relationshipPartPath, id, "An internal relationship target cannot be an absolute URI.", issues, null);
                 }
+                if (rootRelativeTarget)
+                {
+                    targetUri = new Uri(target, UriKind.Relative);
+                }
                 Uri sourceUri = new Uri("/" + sourcePartPath, UriKind.Relative);
                 Uri resolvedTargetUri = PackUriHelper.ResolvePartUri(sourceUri, targetUri);
                 resolvedTargetPath = resolvedTargetUri.OriginalString.TrimStart('/');