gistfile.patch

diff --git a/lib/arborist/build-ideal-tree.js b/lib/arborist/build-ideal-tree.js
index 49b21ca2..d2ed2b35 100644
--- a/lib/arborist/build-ideal-tree.js
+++ b/lib/arborist/build-ideal-tree.js
@@ -1631,52 +1631,66 @@ This is a one-time fix-up, please be patient...
         // placed here as well.  the virtualRoot already has the appropriate
         // overrides applied.
         if (peerEntryEdge) {
-          const peerSet = getPeerSet(current)
-          OUTER: for (const p of peerSet) {
-            // if any have a non-peer dep from the target, or a peer dep if
-            // the target is root, then cannot safely replace and dupe deeper.
+          const currentPeerSet = getPeerSet(current)
+
+          // We are effectively replacing currentPeerSet with newPeerSet
+          // If there are any non-peer deps coming into the currentPeerSet,
+          // which are currently valid, and are from the target, then that
+          // means that we have to ensure that they're not going to be made
+          // invalid by putting the newPeerSet in place.
+          // If the edge comes from somewhere deeper than the target, then
+          // that's fine, because we'll create an invalid edge, detect it,
+          // and duplicate the node further into the tree.
+          // loop through the currentPeerSet checking for valid edges on
+          // the members of the peer set which will be made invalid.
+          const targetEdges = new Set()
+          for (const p of currentPeerSet) {
             for (const edge of p.edgesIn) {
-              if (peerSet.has(edge.from))
+              // edge from within the peerSet, ignore
+              if (currentPeerSet.has(edge.from))
                 continue
-
-              // only respect valid edges, however, since we're likely trying
-              // to fix the very one that's currently broken!  If the virtual
-              // root's replacement is ok, and doesn't have any invalid edges
-              // indicating that it was an overridden peer, then ignore the
-              // conflict and continue.  If it WAS an override, then we need
-              // to get the conflict here so that we can decide whether to
-              // accept the current dep node, clobber it, or fail the install.
-              if (edge.from === target && edge.valid) {
-                // replacement from virtual root
-                const rep = dep.parent.children.get(edge.name)
-                // not going to replace it, so make sure it won't cause problems
-                // if the things we ARE replacing are going to break the edges
-                // for the thing that has to be here, then it's a conflict.
-                if (!rep) {
-                  const current = edge.to
-                  for (const repEdge of current.edgesOut.values()) {
-                    const newRepDep = dep.parent.children.get(repEdge.name)
-                    if (repEdge.valid && newRepDep && !newRepDep.satisfies(repEdge)) {
-                      canReplace = false
-                      break OUTER
-                    }
-                  }
-                  continue
+              // only care about valid edges from target.
+              // edges from elsewhere can dupe if offended, invalid edges
+              // are already being fixed or will be later.
+              if (edge.from !== target || !edge.valid)
+                continue
+              targetEdges.add(edge)
+            }
+          }
+          debug.log('targetEdges', dep.name, targetEdges)
+          for (const edge of targetEdges) {
+            // see if we intend to replace this one anyway
+            const rep = dep.parent.children.get(edge.name)
+            const current = edge.to
+            if (!rep) {
+              debug.log('no rep', edge)
+              // this isn't one we're replacing.  but it WAS included in the
+              // peerSet for some reason, so make sure that it's still
+              // ok with the replacements in the new peerSet
+              for (const curEdge of current.edgesOut.values()) {
+                const newRepDep = dep.parent.children.get(curEdge.name)
+                if (curEdge.valid && newRepDep && !newRepDep.satisfies(curEdge)) {
+                  debug.log('not satisfied', curEdge, newRepDep)
+                  canReplace = false
+                  break
                 }
-
-                // was said replacement an override already?
-                const override = [...rep.edgesIn].some(e => !e.valid)
-                // if we have a rep, and it's ok to put in this location, and
-                // it's not already part of an override in the peerSet, then
-                // we can continue with it.
-                if (rep.satisfies(edge) && !override)
-                  continue
-
-                // Otherwise, we cannot replace.
-                canReplace = false
-                break OUTER
               }
+              continue
             }
+
+            debug.log('have replacement', rep)
+
+            // was this replacement already an override of some sort?
+            const override = [...rep.edgesIn].some(e => !e.valid)
+            // if we have a rep, and it's ok to put in this location, and
+            // it's not already part of an override in the peerSet, then
+            // we can continue with it.
+            if (rep.satisfies(edge) && !override)
+              continue
+            // Otherwise, we cannot replace.
+            debug.log('cannot replace', edge, rep)
+            canReplace = false
+            break
           }
         }
         if (canReplace) {