--- dyld/dyld-519.2.1/dyld3/shared-cache/OptimizerLinkedit.cpp
+++ dyld/dyld-551.4/dyld3/shared-cache/OptimizerLinkedit.cpp
@@ -296,9 +296,10 @@
         DepNode& node = _depDAG[op->machHeader()];
         for (const char* depPath : op->getDownwardDependents()) {
             macho_header<P>* depMH = _dylibPathToMachHeader[depPath];
-            assert(depMH != NULL);
-            DepNode* depNode = &_depDAG[depMH];
-            node._dependents.push_back(depNode);
+            if ( depMH != nullptr ) {
+                DepNode* depNode = &_depDAG[depMH];
+                node._dependents.push_back(depNode);
+            }
         }
     }