diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index d09db82fc..3fe01270e 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -2065,7 +2065,9 @@ void DerivationGoal::startBuilder()
             if (!found)
                 throw Error(format("derivation '%1%' requested impure path '%2%', but it was not in allowed-impure-host-deps") % drvPath % i);
 
-            dirsInChroot[i] = i;
+            /* Allow files in __impureHostDeps to be missing; e.g.
+               macOS 11+ has no /usr/lib/libSystem*.dylib */
+            dirsInChroot[i] = {i, true};
         }
 
 #if __linux__