diff --git a/.changeset/kind-feet-swim.md b/.changeset/kind-feet-swim.md
new file mode 100644
index 000000000000..fb3840e878dd
--- /dev/null
+++ b/.changeset/kind-feet-swim.md
@@ -0,0 +1,6 @@
+---
+swc_core: patch
+swc_ecma_minifier: patch
+---
+
+fix(es/minifier): Set param type to unknown
diff --git a/crates/swc_ecma_minifier/src/program_data.rs b/crates/swc_ecma_minifier/src/program_data.rs
index cc2053a91c8a..df8e6c3dfb17 100644
--- a/crates/swc_ecma_minifier/src/program_data.rs
+++ b/crates/swc_ecma_minifier/src/program_data.rs
@@ -449,7 +449,12 @@ impl Storage for ProgramData {
         }
 
         v.var_initialized |= init_type.is_some();
-        v.merged_var_type.merge(init_type);
+
+        if ctx.in_pat_of_param {
+            v.merged_var_type = Some(Value::Unknown);
+        } else {
+            v.merged_var_type.merge(init_type);
+        }
 
         v.declared_count += 1;
         v.declared = true;
diff --git a/crates/swc_ecma_minifier/tests/fixture/issues/8718/7/input.js b/crates/swc_ecma_minifier/tests/fixture/issues/8718/7/input.js
new file mode 100644
index 000000000000..3d2b497fc358
--- /dev/null
+++ b/crates/swc_ecma_minifier/tests/fixture/issues/8718/7/input.js
@@ -0,0 +1,6 @@
+export function foo(a) {
+    a += 1;
+    a += 2;
+
+    return a;
+}
diff --git a/crates/swc_ecma_minifier/tests/fixture/issues/8718/7/output.js b/crates/swc_ecma_minifier/tests/fixture/issues/8718/7/output.js
new file mode 100644
index 000000000000..3460da26e4d4
--- /dev/null
+++ b/crates/swc_ecma_minifier/tests/fixture/issues/8718/7/output.js
@@ -0,0 +1,3 @@
+export function foo(a) {
+    return a += 1, a += 2;
+}