diff --git a/.gitattributes b/.gitattributes
index bf494b31916fe9..b7335e3dfff63f 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -27,8 +27,13 @@
 *.cmd text eol=crlf
 *.bat text eol=crlf
 
-*.cs text diff=csharp
-*.vb text
+# Force managed source files to lf in the working tree so the source-document
+# checksums the compiler records in portable PDBs match the lf blobs SourceLink
+# serves from GitHub raw URLs. Without eol=lf, Windows build checkouts produce
+# crlf source, making strict SourceLink/PDB byte verification fail even though
+# the content matches after line-ending normalization. See dotnet/runtime#129023.
+*.cs text eol=lf diff=csharp
+*.vb text eol=lf
 *.resx text
 *.c text
 *.cpp text
@@ -53,8 +58,8 @@
 *.m text
 *.asm text
 *.erl text
-*.fs text
-*.fsx text
+*.fs text eol=lf
+*.fsx text eol=lf
 *.hs text
 
 *.csproj text