diff --git a/src/jsifier.js b/src/jsifier.js
index 7522d471bf783..a0597907cc345 100644
--- a/src/jsifier.js
+++ b/src/jsifier.js
@@ -55,9 +55,8 @@ function JSify(data, functionsOnly) {
   if (mainPass) {
     // Add additional necessary items for the main pass. We can now do this since types are parsed (types can be used through
     // generateStructInfo in library.js)
-    //B.start('jsifier-libload');
+
     LibraryManager.load();
-    //B.stop('jsifier-libload');
 
     var libFuncsToInclude;
     if (INCLUDE_FULL_LIBRARY) {
@@ -68,10 +67,6 @@ function JSify(data, functionsOnly) {
           libFuncsToInclude.push(key);
         }
       }
-      // mark implemented functions as already added (so if memcpy is in the forced full JS library, but also done in C, we just need the C)
-      for (var added in IMPLEMENTED_FUNCTIONS) {
-        addedLibraryItems[added.substr(1)] = true;
-      }
     } else {
       libFuncsToInclude = DEFAULT_LIBRARY_FUNCS_TO_INCLUDE;
     }
@@ -134,6 +129,13 @@ function JSify(data, functionsOnly) {
         var finalName = '_' + ident;
       }
 
+      // if the function was implemented in compiled code, we just need to export it so we can reach it from JS
+      if (finalName in IMPLEMENTED_FUNCTIONS) {
+        EXPORTED_FUNCTIONS[finalName] = 1;
+        // stop here: we don't need to add anything from our js libraries, not even deps, compiled code is on it
+        return '';
+      }
+
       // Don't replace implemented functions with library ones (which can happen when we add dependencies).
       // Note: We don't return the dependencies here. Be careful not to end up where this matters
       if (finalName in Functions.implementedFunctions) return '';
diff --git a/tests/test_core.py b/tests/test_core.py
index 99439fe649b2f..b4d8bed343700 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -4741,6 +4741,38 @@ def test_unicode_js_library(self):
     self.emcc_args += ['--js-library', path_from_root('tests', 'unicode_library.js')]
     self.do_run(open(os.path.join(self.get_dir(), 'main.cpp'), 'r').read(), u'Unicode snowman \u2603 says hello!')
 
+  def test_js_lib_dep_memset(self):
+    open('lib.js', 'w').write(r'''
+mergeInto(LibraryManager.library, {
+  depper__deps: ['memset'],
+  depper: function(ptr) {
+    _memset(ptr, 'd'.charCodeAt(0), 10);
+  },
+});
+''')
+    src = r'''
+#include <string.h>
+#include <stdio.h>
+
+extern "C" {
+extern void depper(char*);
+}
+
+int main(int argc, char** argv) {
+  char buffer[11];
+  buffer[10] = '\0';
+  // call by a pointer, to force linking of memset, no llvm intrinsic here
+  volatile auto ptr = memset;
+  (*ptr)(buffer, 'a', 10);
+  depper(buffer);
+  puts(buffer);
+}
+'''
+    self.emcc_args += ['--js-library', 'lib.js']
+    self.do_run(src, 'dddddddddd')
+    Settings.INCLUDE_FULL_LIBRARY = 1
+    self.do_run(src, 'dddddddddd')
+
   def test_funcptr_import_type(self):
     self.emcc_args += ['--js-library', path_from_root('tests', 'core', 'test_funcptr_import_type.js'), '-std=c++11']
     self.do_run_in_out_file_test('tests', 'core', 'test_funcptr_import_type')