diff --git a/src/main.cpp b/src/main.cpp
index e41e856..16b1cf9 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -714,6 +714,14 @@ int main(int argc, char* argv[]) {
                 return 1;
             }
 
+            if (!plan.conflicts.empty()) {
+                std::cerr << "error: package conflicts detected:\n";
+                for (auto& c : plan.conflicts) {
+                    std::cerr << "  " << c << "\n";
+                }
+                return 1;
+            }
+
             std::cout << plan.steps.size() << " packages in build order:\n";
             for (auto& step : plan.steps) {
                 std::cout << "  " << step.name << " (" << step.dependencies.size()
@@ -781,6 +789,11 @@ int main(int argc, char* argv[]) {
                 for (auto& c : plan.cycles) std::cerr << "  " << c << "\n";
                 return 1;
             }
+            if (!plan.conflicts.empty()) {
+                std::cerr << "error: package conflicts detected:\n";
+                for (auto& c : plan.conflicts) std::cerr << "  " << c << "\n";
+                return 1;
+            }
             if (plan.steps.empty()) {
                 std::cout << "nothing to build\n";
                 return 0;