diff --git a/src/Bundle.js b/src/Bundle.js
index 1d3255b..0a670d2 100644
--- a/src/Bundle.js
+++ b/src/Bundle.js
@@ -82,17 +82,15 @@ export default class Bundle {
 				});
 
 				// mark statements that should appear in the bundle
+				const safe = !this.aggressive;
+
 				let settled = false;
 				while ( !settled ) {
 					settled = true;
 
-					if ( this.aggressive ) {
-						settled = !entryModule.run();
-					} else {
-						this.modules.forEach( module => {
-							if ( module.run() ) settled = false;
-						});
-					}
+					this.modules.forEach( module => {
+						if ( module.run( safe || module === entryModule ) ) settled = false;
+					});
 				}
 
 				// Phase 4 – final preparation. We order the modules with an
diff --git a/src/Declaration.js b/src/Declaration.js
index 03a5b17..bc343ea 100644
--- a/src/Declaration.js
+++ b/src/Declaration.js
@@ -39,14 +39,14 @@ export default class Declaration {
 		return `exports.${this.name}`;
 	}
 
-	run ( strongDependencies ) {
+	run ( strongDependencies, safe ) {
 		if ( this.tested ) return this.hasSideEffects;
 		this.tested = true;
 
 		if ( !this.statement || !this.functionNode ) {
 			this.hasSideEffects = true; // err on the side of caution. TODO handle unambiguous `var x; x = y => z` cases
 		} else {
-			this.hasSideEffects = run( this.functionNode.body, this.functionNode._scope, this.statement, strongDependencies );
+			this.hasSideEffects = run( this.functionNode.body, this.functionNode._scope, this.statement, strongDependencies, false, safe );
 		}
 
 		return this.hasSideEffects;
@@ -93,13 +93,13 @@ export class SyntheticDefaultDeclaration {
 			this.original.render();
 	}
 
-	run ( strongDependencies ) {
+	run ( strongDependencies, safe ) {
 		if ( this.original ) {
-			return this.original.run( strongDependencies );
+			return this.original.run( strongDependencies, safe );
 		}
 
 		if ( /FunctionExpression/.test( this.node.declaration.type ) ) {
-			return run( this.node.declaration.body, this.statement.scope, this.statement, strongDependencies );
+			return run( this.node.declaration.body, this.statement.scope, this.statement, strongDependencies, false, safe );
 		}
 	}
 
diff --git a/src/Module.js b/src/Module.js
index 1c50b10..e1965ab 100644
--- a/src/Module.js
+++ b/src/Module.js
@@ -559,11 +559,11 @@ export default class Module {
 		return magicString.trim();
 	}
 
-	run () {
+	run ( safe ) {
 		let marked = false;
 
 		this.statements.forEach( statement => {
-			marked = marked || statement.run( this.strongDependencies );
+			marked = marked || statement.run( this.strongDependencies, safe );
 		});
 
 		return marked;
diff --git a/src/Statement.js b/src/Statement.js
index f374a2b..b4a707e 100644
--- a/src/Statement.js
+++ b/src/Statement.js
@@ -159,11 +159,11 @@ export default class Statement {
 		});
 	}
 
-	run ( strongDependencies ) {
+	run ( strongDependencies, safe ) {
 		if ( ( this.ran && this.isIncluded ) || this.isImportDeclaration || this.isFunctionDeclaration ) return;
 		this.ran = true;
 
-		if ( run( this.node, this.scope, this, strongDependencies ) ) {
+		if ( run( this.node, this.scope, this, strongDependencies, false, safe ) ) {
 			this.mark();
 			return true;
 		}
diff --git a/src/utils/run.js b/src/utils/run.js
index 1f97b5c..8139a40 100644
--- a/src/utils/run.js
+++ b/src/utils/run.js
@@ -46,7 +46,7 @@ simdTypes.forEach( t => {
 
 
 
-export default function run ( node, scope, statement, strongDependencies, force ) {
+export default function run ( node, scope, statement, strongDependencies, force, safe ) {
 	let hasSideEffect = false;
 
 	walk( node, {
@@ -60,7 +60,9 @@ export default function run ( node, scope, statement, strongDependencies, force
 
 				if ( flattened.name === 'arguments' ) {
 					hasSideEffect = true;
-				} if ( !scope.contains( flattened.name ) ) {
+				}
+
+				else if ( !scope.contains( flattened.name ) ) {
 					const declaration = statement.module.trace( flattened.name );
 					if ( declaration && !declaration.isExternal ) {
 						const module = declaration.module || declaration.statement.module; // TODO is this right?
@@ -81,10 +83,10 @@ export default function run ( node, scope, statement, strongDependencies, force
 					                    statement.module.trace( node.callee.name );
 
 					if ( declaration ) {
-						if ( declaration.isExternal || declaration.run( strongDependencies ) ) {
+						if ( declaration.isExternal || declaration.run( strongDependencies, safe ) ) {
 							hasSideEffect = true;
 						}
-					} else if ( !pureFunctions[ node.callee.name ] ) {
+					} else if ( safe && !pureFunctions[ node.callee.name ] ) {
 						hasSideEffect = true;
 					}
 				}
@@ -97,7 +99,7 @@ export default function run ( node, scope, statement, strongDependencies, force
 						// TODO make pureFunctions configurable
 						const declaration = scope.findDeclaration( flattened.name ) || statement.module.trace( flattened.name );
 
-						if ( !!declaration || !pureFunctions[ flattened.keypath ] ) {
+						if ( safe && ( !!declaration || !pureFunctions[ flattened.keypath ] ) ) {
 							hasSideEffect = true;
 						}
 					} else {
@@ -108,7 +110,7 @@ export default function run ( node, scope, statement, strongDependencies, force
 				}
 
 				// otherwise we're probably dealing with a function expression
-				else if ( run( node.callee, scope, statement, strongDependencies, true ) ) {
+				else if ( run( node.callee, scope, statement, strongDependencies, true, safe ) ) {
 					hasSideEffect = true;
 				}
 			}
@@ -124,7 +126,7 @@ export default function run ( node, scope, statement, strongDependencies, force
 				} else {
 					declaration = statement.module.trace( subject.name );
 
-					if ( !declaration || declaration.isExternal || declaration.isUsed ) {
+					if ( ( safe && ( !declaration || declaration.isExternal ) ) || declaration && declaration.isUsed ) {
 						hasSideEffect = true;
 					}
 				}
diff --git a/test/function/aggressive-mode/_config.js b/test/function/aggressive-mode/_config.js
new file mode 100644
index 0000000..7317b3f
--- /dev/null
+++ b/test/function/aggressive-mode/_config.js
@@ -0,0 +1,8 @@
+module.exports = {
+	// solo: true,
+	// show: true,
+	description: 'aggressive mode distinguishes between necessary and probably-not-necessary side-effects',
+	options: {
+		aggressive: true
+	}
+};
diff --git a/test/function/aggressive-mode/foo.js b/test/function/aggressive-mode/foo.js
new file mode 100644
index 0000000..15ed18e
--- /dev/null
+++ b/test/function/aggressive-mode/foo.js
@@ -0,0 +1,11 @@
+function Foo () {}
+
+Foo.prototype = {
+	answer: function () {
+		return 42;
+	}
+};
+
+export default function foo () {
+	return new Foo();
+}
diff --git a/test/function/aggressive-mode/main.js b/test/function/aggressive-mode/main.js
new file mode 100644
index 0000000..707c46a
--- /dev/null
+++ b/test/function/aggressive-mode/main.js
@@ -0,0 +1,3 @@
+import foo from './foo';
+
+assert.equal( foo().answer(), 42 );