diff --git a/main.go b/main.go
index ad5ede3e..bbe7a1e6 100644
--- a/main.go
+++ b/main.go
@@ -55,6 +55,7 @@ type BuildConfig struct {
 	ldFlags       []string
 	tags          string
 	wasmAbi       string
+	heapSize      int64
 	testConfig    compiler.TestConfig
 }
 
@@ -240,10 +241,16 @@ func Compile(pkgName, outpath string, spec *TargetSpec, config *BuildConfig, act
 		// Prepare link command.
 		executable := filepath.Join(dir, "main")
 		tmppath := executable // final file
-		ldflags := append(ldflags, "-o", executable, objfile, "-L", root)
+		ldflags = append(ldflags, "-o", executable, objfile, "-L", root)
 		if spec.RTLib == "compiler-rt" {
 			ldflags = append(ldflags, librt)
 		}
+		if spec.GOARCH == "wasm" {
+			// Round heap size to next multiple of 65536 (the WebAssembly page
+			// size).
+			heapSize := (config.heapSize + (65536 - 1)) &^ (65536 - 1)
+			ldflags = append(ldflags, "--initial-memory="+strconv.FormatInt(heapSize, 10))
+		}
 
 		// Compile extra files.
 		for i, path := range spec.ExtraFiles {
@@ -540,6 +547,30 @@ func Run(pkgName, target string, config *BuildConfig) error {
 	})
 }
 
+// parseSize converts a human-readable size (with k/m/g suffix) into a plain
+// number.
+func parseSize(s string) (int64, error) {
+	s = strings.ToLower(strings.TrimSpace(s))
+	if len(s) == 0 {
+		return 0, errors.New("no size provided")
+	}
+	multiply := int64(1)
+	switch s[len(s)-1] {
+	case 'k':
+		multiply = 1 << 10
+	case 'm':
+		multiply = 1 << 20
+	case 'g':
+		multiply = 1 << 30
+	}
+	if multiply != 1 {
+		s = s[:len(s)-1]
+	}
+	n, err := strconv.ParseInt(s, 0, 64)
+	n *= multiply
+	return n, err
+}
+
 func usage() {
 	fmt.Fprintln(os.Stderr, "TinyGo is a Go compiler for small places.")
 	fmt.Fprintln(os.Stderr, "version:", version)
@@ -598,6 +629,7 @@ func main() {
 	cFlags := flag.String("cflags", "", "additional cflags for compiler")
 	ldFlags := flag.String("ldflags", "", "additional ldflags for linker")
 	wasmAbi := flag.String("wasm-abi", "js", "WebAssembly ABI conventions: js (no i64 params) or generic")
+	heapSize := flag.String("heap-size", "1M", "default heap size in bytes (only supported by WebAssembly)")
 
 	if len(os.Args) < 2 {
 		fmt.Fprintln(os.Stderr, "No command-line arguments supplied.")
@@ -633,6 +665,13 @@ func main() {
 		os.Exit(1)
 	}
 
+	var err error
+	if config.heapSize, err = parseSize(*heapSize); err != nil {
+		fmt.Fprintln(os.Stderr, "Could not read heap size:", *heapSize)
+		usage()
+		os.Exit(1)
+	}
+
 	os.Setenv("CC", "clang -target="+*target)
 
 	switch command {
diff --git a/src/runtime/arch_wasm.go b/src/runtime/arch_wasm.go
index 1015fe11..71d6724b 100644
--- a/src/runtime/arch_wasm.go
+++ b/src/runtime/arch_wasm.go
@@ -14,9 +14,12 @@ const TargetBits = 32
 //go:extern __heap_base
 var heapStartSymbol unsafe.Pointer
 
+//go:export llvm.wasm.memory.size.i32
+func wasm_memory_size(index int32) int32
+
 var (
 	heapStart = uintptr(unsafe.Pointer(&heapStartSymbol))
-	heapEnd   = (heapStart + wasmPageSize - 1) &^ (wasmPageSize - 1) // conservative guess: one page of heap memory
+	heapEnd   = uintptr(wasm_memory_size(0) * wasmPageSize)
 )
 
 const wasmPageSize = 64 * 1024