diff --git a/blender_asset_tracer/bpathlib.py b/blender_asset_tracer/bpathlib.py
index 3e3f592..170aae6 100644
--- a/blender_asset_tracer/bpathlib.py
+++ b/blender_asset_tracer/bpathlib.py
@@ -87,17 +87,19 @@ class BlendPath(bytes):
     def to_path(self) -> pathlib.PurePath:
         """Convert this path to a pathlib.PurePath.
 
+        This path MUST NOT be a blendfile-relative path (e.g. it may not start
+        with `//`). For such paths, first use `.absolute()` to resolve the path.
+
         Interprets the path as UTF-8, and if that fails falls back to the local
         filesystem encoding.
-
-        Note that this does not handle blend-file-relative paths specially, so
-        the returned Path may still start with '//'.
         """
         # TODO(Sybren): once we target Python 3.6, implement __fspath__().
         try:
             decoded = self.decode('utf8')
         except UnicodeDecodeError:
             decoded = self.decode(sys.getfilesystemencoding())
+        if self.is_blendfile_relative():
+            raise ValueError('to_path() cannot be used on blendfile-relative paths')
         return pathlib.PurePath(decoded)
 
     def is_blendfile_relative(self) -> bool:
diff --git a/blender_asset_tracer/trace/file2blocks.py b/blender_asset_tracer/trace/file2blocks.py
index 97fb506..b45d7b7 100644
--- a/blender_asset_tracer/trace/file2blocks.py
+++ b/blender_asset_tracer/trace/file2blocks.py
@@ -110,7 +110,7 @@ class BlockIterator:
         # We've gone through all the blocks in this file, now open the libraries
         # and iterate over the blocks referred there.
         for lib_bpath, idblocks in blocks_per_lib.items():
-            lib_path = lib_bpath.to_path()
+            lib_path = pathlib.Path(lib_bpath.to_path())
             try:
                 lib_path = lib_path.resolve()
             except FileNotFoundError: