diff --git a/fdroidserver/common.py b/fdroidserver/common.py
index 960d06ca..18148018 100644
--- a/fdroidserver/common.py
+++ b/fdroidserver/common.py
@@ -1460,7 +1460,10 @@ def scan_source(build_dir, root_dir, thisbuild):
             if toignore(fd):
                 continue
 
-            mime = magic.from_file(fp, mime=True) if ms is None else ms.file(fp)
+            try:
+                mime = magic.from_file(fp, mime=True) if ms is None else ms.file(fp)
+            except UnicodeError:
+                warnproblem('malformed magic number', fd, fp)
 
             if mime == 'application/x-sharedlib':
                 count += handleproblem('shared library', fd, fp)