diff --git a/src/libstore/build/drv-output-substitution-goal.cc b/src/libstore/build/drv-output-substitution-goal.cc
index ec3a8d758..be270d079 100644
--- a/src/libstore/build/drv-output-substitution-goal.cc
+++ b/src/libstore/build/drv-output-substitution-goal.cc
@@ -65,9 +65,14 @@ void DrvOutputSubstitutionGoal::tryNext()
             if (auto localOutputInfo = worker.store.queryRealisation(depId);
                 localOutputInfo && localOutputInfo->outPath != depPath) {
                 warn(
-                    "substituter '%s' has an incompatible realisation for '%s', ignoring",
+                    "substituter '%s' has an incompatible realisation for '%s', ignoring.\n"
+                    "Local:  %s\n"
+                    "Remote: %s",
                     sub->getUri(),
-                    depId.to_string());
+                    depId.to_string(),
+                    worker.store.printStorePath(localOutputInfo->outPath),
+                    worker.store.printStorePath(depPath)
+                );
                 tryNext();
                 return;
             }
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 064f7a432..d7c7f8e1d 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -732,8 +732,13 @@ void LocalStore::registerDrvOutput(const Realisation & info)
                     .exec();
             } else {
                 throw Error("Trying to register a realisation of '%s', but we already "
-                            "have another one locally",
-                    info.id.to_string());
+                            "have another one locally.\n"
+                            "Local:  %s\n"
+                            "Remote: %s",
+                    info.id.to_string(),
+                    printStorePath(oldR->outPath),
+                    printStorePath(info.outPath)
+                );
             }
         } else {
             state->stmts->RegisterRealisedOutput.use()