diff --git a/asm.js b/asm.js
index 5099352..d10eedb 100644
--- a/asm.js
+++ b/asm.js
@@ -708,6 +708,7 @@ export class Assembler {
         this.data = [];
         this.defs = {};
         this.blocks = [];
+        this.types = [];
 	}
 
     action_append(action) {
@@ -899,19 +900,8 @@ export class Assembler {
     }
 
     wasm_section_type() {
-        const funcs = Object.values(this.funcs);
-        if (funcs.length == 0) return null;
-        const contents = funcs.map(({ params, results }) => {
-            const param_types = Object.values(params);
-            return [
-                types["func"],
-                param_types.length,
-                ...param_types,
-                results.length,
-                ...results,
-            ];
-        });
-        return [ contents.length ].concat(...contents);
+        if (this.types.length == 0) return null;
+        return [ this.types.length ].concat(...this.types);
     }
 
     wasm_section_import() {
@@ -933,9 +923,10 @@ export class Assembler {
     }
 
     wasm_section_func() {
-        const func_count = Object.entries(this.funcs).length;
-        if (func_count == 0) return null;
-        return [ func_count, ...Array(func_count).keys() ];
+        const types = Object.values(this.funcs).map(({type}) => type);
+        const count = types.length;
+        if (count == 0) return null;
+        return [ count, ...types ];
     }
 
     wasm_section_mem() {
@@ -1014,6 +1005,8 @@ export class Assembler {
     }
 
 	wasm() {
+        this.resolve_func_types();
+
         const template = [
             [ Section.TYPE,   () => this.wasm_section_type() ],
             [ Section.IMPORT, () => this.wasm_section_import() ],
@@ -1038,4 +1031,29 @@ export class Assembler {
         else
             return [ flags, init ];
     }
+
+    func_type({ params, results }) {
+        const param_types = Object.values(params);
+        return [
+            types["func"],
+            param_types.length,
+            ...param_types,
+            results.length,
+            ...results,
+        ];
+    }
+
+    array_eq(a, b) {
+        return a.length == b.length && a.every((x, i) => x == b[i]);
+    }
+
+    ensure_type(type) {
+        const index = this.types.findIndex((t) => this.array_eq(type, t));
+        return index != -1 ? index : this.types.push(type) - 1;
+    }
+
+    resolve_func_types() {
+        for (const func of Object.values(this.funcs))
+            func.type = this.ensure_type(this.func_type(func));
+    }
 }