diff --git a/parse.cm b/parse.cm
index 7e490459..6dc0f54a 100644
--- a/parse.cm
+++ b/parse.cm
@@ -391,7 +391,7 @@ var parse = function(tokens, src, filename, tokenizer) {
               ast_node_end(param)
               if (tok.kind == "=" || tok.kind == "|") {
                 advance()
-                param.expression = parse_expr()
+                param.expression = parse_assign_expr()
               }
               push(params, param)
             } else {
diff --git a/parse.mach b/parse.mach
index 76d89a78..03761786 100644
Binary files a/parse.mach and b/parse.mach differ
diff --git a/vm_suite.ce b/vm_suite.ce
index 7bbeb573..9ddc0d26 100644
--- a/vm_suite.ce
+++ b/vm_suite.ce
@@ -3671,6 +3671,167 @@ run("functino >>>! unsigned shift right", function() {
   assert_eq(>>>!(-1, 28), 15, ">>>! unsigned shift right")
 })
 
+// ============================================================================
+// FUNCTION DEFAULT PARAMETERS
+// ============================================================================
+
+run("default param basic", function() {
+  var fn = function(a = 3, b = 5) { return a + b }
+  assert_eq(fn(), 8, "both defaults")
+  assert_eq(fn(10), 15, "first provided")
+  assert_eq(fn(10, 20), 30, "both provided")
+})
+
+run("default param null triggers default", function() {
+  var fn = function(a = 99) { return a }
+  assert_eq(fn(null), 99, "null should trigger default")
+  assert_eq(fn(), 99, "missing should trigger default")
+  assert_eq(fn(0), 0, "zero should not trigger default")
+  assert_eq(fn(false), false, "false should not trigger default")
+  assert_eq(fn(""), "", "empty string should not trigger default")
+})
+
+run("default param pipe syntax", function() {
+  var fn = function(a | 3, b | 5) { return a + b }
+  assert_eq(fn(), 8, "pipe both defaults")
+  assert_eq(fn(10), 15, "pipe first provided")
+  assert_eq(fn(10, 20), 30, "pipe both provided")
+})
+
+run("default param object literal", function() {
+  var fn = function(a = {x: 1, y: 2}) { return a.x + a.y }
+  assert_eq(fn(), 3, "object default")
+  assert_eq(fn({x: 10, y: 20}), 30, "object provided")
+})
+
+run("default param array literal", function() {
+  var fn = function(a = [10, 20, 30]) { return a[1] }
+  assert_eq(fn(), 20, "array default")
+  assert_eq(fn([99]), null, "array provided")
+})
+
+run("default param nested object", function() {
+  var fn = function(a = {inner: {val: 42}}) { return a.inner.val }
+  assert_eq(fn(), 42, "nested object default")
+})
+
+run("default param expression", function() {
+  var fn = function(a = 1 + 2, b = 3 * 4) { return a + b }
+  assert_eq(fn(), 15, "expression defaults")
+})
+
+run("default param negative number", function() {
+  var fn = function(a = -1) { return a }
+  assert_eq(fn(), -1, "negative default")
+})
+
+run("default param function call", function() {
+  var double = function(x) { return x * 2 }
+  var fn = function(a = double(21)) { return a }
+  assert_eq(fn(), 42, "function call default")
+})
+
+run("default param function value", function() {
+  var fn = function(f = function() { return 42 }) { return f() }
+  assert_eq(fn(), 42, "function as default")
+})
+
+run("default param arrow function", function() {
+  var fn = function(f = (x) => x * 2) { return f(5) }
+  assert_eq(fn(), 10, "arrow function as default")
+})
+
+run("default param ternary in default", function() {
+  var fn = function(a = true ? 10 : 20) { return a }
+  assert_eq(fn(), 10, "ternary default")
+})
+
+run("default param string with comma", function() {
+  var fn = function(a = "hello, world") { return a }
+  assert_eq(fn(), "hello, world", "string comma default")
+})
+
+run("default param empty object", function() {
+  var fn = function(a = {}) { return is_object(a) }
+  assert_eq(fn(), true, "empty object default")
+})
+
+run("default param empty array", function() {
+  var fn = function(a = []) { return is_array(a) }
+  assert_eq(fn(), true, "empty array default")
+})
+
+run("default param multiple complex", function() {
+  var fn = function(a = {k: 1}, b = [4, 5], c = "hi") {
+    return text(a.k) + text(b[0]) + c
+  }
+  assert_eq(fn(), "14hi", "multiple complex defaults")
+  assert_eq(fn({k: 9}), "94hi", "first overridden")
+  assert_eq(fn({k: 9}, [7]), "97hi", "first two overridden")
+  assert_eq(fn({k: 9}, [7], "yo"), "97yo", "all overridden")
+})
+
+run("default param independent defaults", function() {
+  var fn = function(a = 1, b = 2) { return a + b }
+  assert_eq(fn(), 3, "both defaults")
+  assert_eq(fn(10), 12, "first provided")
+})
+
+run("default param arrow function syntax", function() {
+  var fn = (a = 7, b = 8) => a + b
+  assert_eq(fn(), 15, "arrow defaults")
+  assert_eq(fn(100), 108, "arrow first provided")
+  assert_eq(fn(100, 200), 300, "arrow both provided")
+})
+
+run("default param single arrow", function() {
+  var fn = (a = 42) => a
+  assert_eq(fn(), 42, "single arrow default")
+  assert_eq(fn(0), 0, "single arrow zero")
+})
+
+run("default param method shorthand", function() {
+  var obj = {
+    calc(a = 10, b = 20) {
+      return a + b
+    }
+  }
+  assert_eq(obj.calc(), 30, "method defaults")
+  assert_eq(obj.calc(1), 21, "method first provided")
+  assert_eq(obj.calc(1, 2), 3, "method both provided")
+})
+
+run("default param each fresh object", function() {
+  var fn = function(a = {count: 0}) {
+    a.count = a.count + 1
+    return a.count
+  }
+  assert_eq(fn(), 1, "first call fresh object")
+  assert_eq(fn(), 1, "second call fresh object")
+})
+
+run("default param each fresh array", function() {
+  var fn = function(a = []) {
+    a[] = 1
+    return length(a)
+  }
+  assert_eq(fn(), 1, "first call fresh array")
+  assert_eq(fn(), 1, "second call fresh array")
+})
+
+run("default param nested parens", function() {
+  var fn = function(a = (1 + 2) * 3) { return a }
+  assert_eq(fn(), 9, "nested parens default")
+})
+
+run("default param closure over outer", function() {
+  var base = 100
+  var fn = function(a = base) { return a }
+  assert_eq(fn(), 100, "closure over outer")
+  base = 200
+  assert_eq(fn(), 200, "closure sees updated outer")
+})
+
 // ============================================================================
 // SUMMARY
 // ============================================================================