diff --git a/spec/model/implementation/effective-module-specification.spec.ts b/spec/model/implementation/effective-module-specification.spec.ts
new file mode 100644
index 00000000..220499ca
--- /dev/null
+++ b/spec/model/implementation/effective-module-specification.spec.ts
@@ -0,0 +1,70 @@
+import {
+    EffectiveModuleSpecification,
+    EffectiveModuleSpecificationClause,
+} from '../../../src/model/implementation/modules/effective-module-specification';
+import { expect } from 'chai';
+
+describe('EffectiveModuleSpecification', () => {
+    describe('simplify()', () => {
+        it('removes duplicate simple clauses', () => {
+            const input = new EffectiveModuleSpecification({
+                orCombinedClauses: [
+                    new EffectiveModuleSpecificationClause({ andCombinedModules: ['a'] }),
+                    new EffectiveModuleSpecificationClause({ andCombinedModules: ['b'] }),
+                    new EffectiveModuleSpecificationClause({ andCombinedModules: ['a'] }),
+                ],
+            });
+            const output = input.simplify();
+            expect(output.toString()).to.equal('a, b');
+        });
+
+        it('removes duplicate multi-module clauses', () => {
+            const input = new EffectiveModuleSpecification({
+                orCombinedClauses: [
+                    new EffectiveModuleSpecificationClause({ andCombinedModules: ['a', 'c'] }),
+                    new EffectiveModuleSpecificationClause({ andCombinedModules: ['b'] }),
+                    new EffectiveModuleSpecificationClause({ andCombinedModules: ['a', 'c'] }),
+                ],
+            });
+            const output = input.simplify();
+            expect(output.toString()).to.equal('b, a && c');
+        });
+
+        it('removes redundant clauses', () => {
+            const input = new EffectiveModuleSpecification({
+                orCombinedClauses: [
+                    new EffectiveModuleSpecificationClause({ andCombinedModules: ['a', 'c'] }),
+                    new EffectiveModuleSpecificationClause({ andCombinedModules: ['b'] }),
+                    new EffectiveModuleSpecificationClause({ andCombinedModules: ['a', 'c', 'd'] }),
+                ],
+            });
+            const output = input.simplify();
+            expect(output.toString()).to.equal('b, a && c');
+        });
+
+        it('works with a more complicated case', () => {
+            const input = new EffectiveModuleSpecification({
+                orCombinedClauses: [
+                    new EffectiveModuleSpecificationClause({ andCombinedModules: ['shipping'] }),
+                    new EffectiveModuleSpecificationClause({
+                        andCombinedModules: ['shipping', 'dangerous_goods'],
+                    }),
+                    new EffectiveModuleSpecificationClause({
+                        andCombinedModules: ['tms', 'dangerous_goods'],
+                    }),
+                    new EffectiveModuleSpecificationClause({
+                        andCombinedModules: ['shipping', 'dangerous_goods', 'extra1'],
+                    }),
+                    new EffectiveModuleSpecificationClause({
+                        andCombinedModules: ['tms', 'dangerous_goods', 'extra1'],
+                    }),
+                    new EffectiveModuleSpecificationClause({
+                        andCombinedModules: ['extra1'],
+                    }),
+                ],
+            });
+            const output = input.simplify();
+            expect(output.toString()).to.equal('extra1, shipping, dangerous_goods && tms');
+        });
+    });
+});
diff --git a/src/model/implementation/modules/effective-module-specification.ts b/src/model/implementation/modules/effective-module-specification.ts
index 7ceb6802..e3b42fa0 100644
--- a/src/model/implementation/modules/effective-module-specification.ts
+++ b/src/model/implementation/modules/effective-module-specification.ts
@@ -29,18 +29,33 @@ export class EffectiveModuleSpecification {
     }
 
     /**
-     * Sorts the clauses by name and removes duplicates
+     * Sorts the clauses by name and removes duplicates and redundant clauses (e.g. ["a", "a && b"] is simplified to ["a"])
      */
     simplify(): EffectiveModuleSpecification {
-        const map = new Map(
-            this.orCombinedClauses.map((clause) => {
-                const normalized = clause.normalize();
-                return [normalized.toString(), normalized];
-            }),
-        );
-        const keys = Array.from(map.keys()).sort();
-        const normalizedClauses = keys.map((k) => map.get(k)!);
-        return new EffectiveModuleSpecification({ orCombinedClauses: normalizedClauses });
+        // sort by length so we prefer shorter clauses
+        // sort by toString() secondarily to get a normalized representation
+        const clausesSortedByLength = this.orCombinedClauses
+            .map((c) => c.normalize())
+            .sort((a, b) => a.toString().localeCompare(b.toString()))
+            .sort((a, b) => a.andCombinedModules.length - b.andCombinedModules.length);
+        const nonRedundantClauses: EffectiveModuleSpecificationClause[] = [];
+        // this has quadratic runtime w.r.t. number atoms, but we don't expect huge module specifications
+        for (const clause of clausesSortedByLength) {
+            const modulesInClause = new Set(clause.andCombinedModules);
+            let clauseIsRedundant = false;
+            for (const existingClause of nonRedundantClauses) {
+                if (existingClause.andCombinedModules.every((m) => modulesInClause.has(m))) {
+                    // existingClause implies clause
+                    clauseIsRedundant = true;
+                    break;
+                }
+            }
+            if (!clauseIsRedundant) {
+                nonRedundantClauses.push(clause);
+            }
+        }
+
+        return new EffectiveModuleSpecification({ orCombinedClauses: nonRedundantClauses });
     }
 
     orCombineWith(other: EffectiveModuleSpecification) {
@@ -68,6 +83,10 @@ export class EffectiveModuleSpecification {
         });
         return combined.simplify();
     }
+
+    toString() {
+        return this.orCombinedClauses.map((c) => c.toString()).join(', ');
+    }
 }
 
 export class EffectiveModuleSpecificationClause {