diff --git a/lld/COFF/Driver.cpp b/lld/COFF/Driver.cpp
--- a/lld/COFF/Driver.cpp
+++ b/lld/COFF/Driver.cpp
@@ -262,6 +262,9 @@
         ec = retryMb.getError();
         if (!ec)
           mb = std::move(*retryMb);
+      } else {
+        // We've already handled this file.
+        return;
       }
     }
     if (ec) {
diff --git a/lld/test/COFF/winsysroot.test b/lld/test/COFF/winsysroot.test
--- a/lld/test/COFF/winsysroot.test
+++ b/lld/test/COFF/winsysroot.test
@@ -26,16 +26,27 @@
 # RUN: lld-link %t.obj /winsysroot:%t.dir/sysroot \
 # RUN:          std32.lib /entry:main
 
+Check that passing a lib from /winsysroot twice is ok
+# RUN: lld-link %p/Inputs/hello64.obj /winsysroot:%t.dir/sysroot \
+# RUN:          std64.lib std64.lib /entry:main
+
+Check unknown library
+# RUN: not lld-link %p/Inputs/hello64.obj /winsysroot:%t.dir/sysroot \
+# RUN:          notfound.lib /entry:main 2>&1 | FileCheck --check-prefix=UNKNOWNLIB %s
+UNKNOWNLIB: could not open 'notfound.lib'
+
 If winsysroot lib appears before we can detect arch we don't find it
 # RUN: not lld-link std64.lib %p/Inputs/hello64.obj /winsysroot:%t.dir/sysroot \
-# RUN:          /entry:main
+# RUN:          /entry:main 2>&1 | FileCheck --check-prefix=NO64 %s
 
 Check we don't choose the wrong arch
 # RUN: not lld-link %t.obj /winsysroot:%t.dir/sysroot \
-# RUN:          std64.lib /entry:main
+# RUN:          std64.lib /entry:main 2>&1 | FileCheck --check-prefix=NO64 %s
+NO64: could not open 'std64.lib'
 
 # RUN: not lld-link %p/Inputs/hello64.obj /winsysroot:%t.dir/sysroot \
-# RUN:          std32.lib /entry:main
+# RUN:          std32.lib /entry:main 2>&1 | FileCheck --check-prefix=NO32 %s
+NO32: could not open 'std32.lib'
 
 Check that when /winsysroot is specified, %LIB% is ignored.
 # RUN: env LIB=foo.dir/sysroot/VC/Tools/MSVC/1.1.1.1/lib/x86 not lld-link %t.obj /winsysroot:%t.dir/doesnotexist /defaultlib:std32 2>&1 | FileCheck -check-prefix=LIBIGNORED %s