diff --git a/src/mono/mono/utils/mono-mmap-wasm.c b/src/mono/mono/utils/mono-mmap-wasm.c
index e19645b90e82f2..b2f417b0860385 100644
--- a/src/mono/mono/utils/mono-mmap-wasm.c
+++ b/src/mono/mono/utils/mono-mmap-wasm.c
@@ -90,12 +90,12 @@ mono_setmmapjit (int flag)
 	/* Ignored on HOST_WASM */
 }
 
-void *sbrk (intptr_t increment);
-
 static void*
 valloc_impl (void *addr, size_t size, int flags, MonoMemAccountType type)
 {
 	void *ptr;
+	int mflags = 0;
+	int prot = prot_from_flags (flags);
 
 	if (!mono_valloc_can_alloc (size))
 		return NULL;
@@ -104,8 +104,14 @@ valloc_impl (void *addr, size_t size, int flags, MonoMemAccountType type)
 		/* emscripten throws an exception on 0 length */
 		return NULL;
 
-	ptr = sbrk (size);
-	if (ptr == 0)
+	mflags |= MAP_ANONYMOUS;
+	mflags |= MAP_PRIVATE;
+
+	BEGIN_CRITICAL_SECTION;
+	ptr = mmap (addr, size, prot, mflags, -1, 0);
+	END_CRITICAL_SECTION;
+
+	if (ptr == MAP_FAILED)
 		return NULL;
 
 	mono_account_mem (type, (ssize_t)size);
@@ -161,7 +167,26 @@ mono_valloc_aligned (size_t size, size_t alignment, int flags, MonoMemAccountTyp
 int
 mono_vfree (void *addr, size_t length, MonoMemAccountType type)
 {
-	g_warning ("mono_vfree not implemented on webassembly; silently failing to free\n");
+	VallocInfo *info = (VallocInfo*)(valloc_hash ? g_hash_table_lookup (valloc_hash, addr) : NULL);
+
+	if (info) {
+		/*
+		 * We are passed the aligned address in the middle of the mapping allocated by
+		 * mono_valloc_align (), free the original mapping.
+		 */
+		BEGIN_CRITICAL_SECTION;
+		munmap (info->addr, info->size);
+		END_CRITICAL_SECTION;
+		g_free (info);
+		g_hash_table_remove (valloc_hash, addr);
+	} else {
+		BEGIN_CRITICAL_SECTION;
+		munmap (addr, length);
+		END_CRITICAL_SECTION;
+	}
+
+	mono_account_mem (type, -(ssize_t)length);
+
 	return 0;
 }