diff --git a/src/cc/backend/codegen_expr.c b/src/cc/backend/codegen_expr.c
index fc8b52e7b..5fc935c4b 100644
--- a/src/cc/backend/codegen_expr.c
+++ b/src/cc/backend/codegen_expr.c
@@ -563,14 +563,20 @@ static VReg *gen_comma(Expr *expr) {
 static VReg *gen_assign_sub(Expr *lhs, Expr *rhs) {
   VReg *src = gen_expr(rhs);
   if (lhs->kind == EX_VAR) {
+    const VarInfo *varinfo = scope_find(lhs->var.scope, lhs->var.name, NULL);
+    assert(varinfo != NULL);
     if (is_prim_type(lhs->type) && !is_global_scope(lhs->var.scope)) {
-      const VarInfo *varinfo = scope_find(lhs->var.scope, lhs->var.name, NULL);
       if (is_local_storage(varinfo)) {
         assert(varinfo->local.vreg != NULL);
         new_ir_mov(varinfo->local.vreg, src, is_unsigned(rhs->type) ? IRF_UNSIGNED : 0);
         return src;
       }
     }
+
+    if ((varinfo->storage & (VS_STATIC | VS_USED)) == VS_STATIC) {
+      // Can be omitted.
+      return src;
+    }
   }
 
   VReg *dst = gen_lval(lhs);
diff --git a/src/wcc/emit_wasm.c b/src/wcc/emit_wasm.c
index 89475dcc0..c2cb5f852 100644
--- a/src/wcc/emit_wasm.c
+++ b/src/wcc/emit_wasm.c
@@ -29,6 +29,7 @@ static void emit_global_number(void *ud, const Type *type, Expr *var, Fixnum off
           v += get_indirect_function_index(var->var.name);
         } else {
           GVarInfo *info = get_gvar_info(var);
+          assert(info != NULL);
           assert(!is_prim_type(info->varinfo->type) || (info->varinfo->storage & VS_REF_TAKEN));
           v += info->non_prim.address;
         }
@@ -116,6 +117,7 @@ static void emit_number(void *ud, const Type *type, Expr *var, Fixnum offset) {
     } else {
       assert(var->kind == EX_VAR);
       const GVarInfo *info = get_gvar_info(var);
+      assert(info != NULL);
       assert(!is_prim_type(info->varinfo->type) || (info->varinfo->storage & VS_REF_TAKEN));
       v += info->non_prim.address;
 
diff --git a/src/wcc/gen_wasm.c b/src/wcc/gen_wasm.c
index f208ae0bd..ffa997868 100644
--- a/src/wcc/gen_wasm.c
+++ b/src/wcc/gen_wasm.c
@@ -482,6 +482,7 @@ static void gen_ref_sub(Expr *expr) {
           ADD_VARUINT32(info->indirect_index);
         } else {
           GVarInfo *info = get_gvar_info(expr);
+          assert(info != NULL);
           ADD_CODE(OP_I32_CONST);
           FuncExtra *extra = curfunc->extra;
           DataStorage *code = extra->code;
@@ -554,6 +555,7 @@ static void gen_var(Expr *expr, bool needval) {
         ADD_ULEB128(vreg->prim.local_index);
       } else {
         GVarInfo *info = get_gvar_info(expr);
+        assert(info != NULL);
         ADD_CODE(OP_GLOBAL_GET);
         FuncExtra *extra = curfunc->extra;
         DataStorage *code = extra->code;
@@ -616,6 +618,7 @@ static void gen_set_to_var(Expr *var) {
   } else {
     assert(!is_global_datsec_var(varinfo, var->var.scope));
     GVarInfo *info = get_gvar_info(var);
+    assert(info != NULL);
     ADD_CODE(OP_GLOBAL_SET);
     FuncExtra *extra = curfunc->extra;
     DataStorage *code = extra->code;
@@ -799,6 +802,7 @@ static void gen_incdec(Expr *expr, bool needval) {
   } else {
     assert(!is_global_datsec_var(varinfo, scope));
     GVarInfo *info = get_gvar_info(target);
+    assert(info != NULL);
     ADD_CODE(OP_GLOBAL_SET);
     ADD_ULEB128(info->prim.index);
     if (needval) {
@@ -823,6 +827,12 @@ static void gen_assign_sub(Expr *lhs, Expr *rhs) {
         gen_set_to_var(lhs);
         break;
       }
+
+      if ((varinfo->storage & (VS_STATIC | VS_USED)) == VS_STATIC) {
+        // Assignment can be omitted.
+        gen_expr(rhs, false);
+        return;
+      }
     }
     gen_lval(lhs);
     gen_expr(rhs, true);
diff --git a/src/wcc/traverse.c b/src/wcc/traverse.c
index e87109f64..a179b258e 100644
--- a/src/wcc/traverse.c
+++ b/src/wcc/traverse.c
@@ -157,7 +157,7 @@ GVarInfo *get_gvar_info(Expr *expr) {
   }
   assert(varinfo != NULL);
   GVarInfo *info = get_gvar_info_from_name(name);
-  if (info == NULL) {
+  if (info == NULL && (!(varinfo->storage & VS_STATIC) || (varinfo->storage & VS_USED))) {
     // Returns dummy.
     info = register_gvar_info(name, varinfo);
     info->flag |= GVF_UNRESOLVED;
@@ -165,7 +165,7 @@ GVarInfo *get_gvar_info(Expr *expr) {
   return info;
 }
 
-#define add_global_var(type, name)  scope_add(global_scope, name, type, 0)
+#define add_global_var(type, name)  scope_add(global_scope, name, type, VS_USED)
 
 void add_builtin_function(const char *str, Type *type, BuiltinFunctionProc *proc,
                           bool add_to_scope) {
@@ -629,7 +629,8 @@ static void traverse_varinfo(VarInfo *varinfo) {
     if (scope_find(global_scope, varinfo->name, NULL) == NULL) {
       // Register into global to output linking information.
       GVarInfo *info = register_gvar_info(varinfo->name, varinfo);
-      info->flag |= GVF_UNRESOLVED;
+      if (info != NULL)
+        info->flag |= GVF_UNRESOLVED;
     }
   }
   if (!(varinfo->storage & (VS_EXTERN | VS_STATIC | VS_ENUM_MEMBER)))
@@ -832,6 +833,7 @@ static void add_builtins(int flag) {
     GVarInfo *info = get_gvar_info_from_name(name);
     if (info == NULL)
       info = register_gvar_info(name, varinfo);
+    assert(info != NULL);
     info->flag |= GVF_UNRESOLVED;
   }
 }
@@ -889,7 +891,9 @@ static bool detect_compile_unit_sp(Function *func) {
 static int detect_compile_unit_memory(void) {
   for (int i = 0, len = global_scope->vars->len; i < len; ++i) {
     VarInfo *varinfo = global_scope->vars->data[i];
-    if (varinfo->storage & (VS_EXTERN | VS_ENUM_MEMBER) || varinfo->type->kind == TY_FUNC)
+    if (varinfo->type->kind == TY_FUNC ||
+        (varinfo->storage & (VS_EXTERN | VS_ENUM_MEMBER)) ||
+        (varinfo->storage & (VS_STATIC | VS_USED)) == VS_STATIC)  // Static variable but not used.
       continue;
     if (is_global_datsec_var(varinfo, global_scope))
       return CUF_LINEAR_MEMORY;
@@ -992,8 +996,8 @@ void traverse_ast(Vector *decls) {
       GVarInfo *info;
       for (int it = 0; (it = table_iterate(&gvar_info_table, it, &name, (void**)&info)) != -1; ) {
         const VarInfo *varinfo = info->varinfo;
-        if (varinfo->storage & VS_ENUM_MEMBER || varinfo->type->kind == TY_FUNC)
-          continue;
+        assert(!(varinfo->storage & VS_ENUM_MEMBER || varinfo->type->kind == TY_FUNC));
+        assert(!((varinfo->storage & (VS_STATIC | VS_USED)) == VS_STATIC));
         if ((k == 0 && !(info->flag & GVF_UNRESOLVED)) ||
             (k != 0 && ((info->flag & GVF_UNRESOLVED) || (varinfo->global.init == NULL) == (k == 1))))
           continue;
diff --git a/tests/test.sh b/tests/test.sh
index 4b2852b69..672a1bb57 100755
--- a/tests/test.sh
+++ b/tests/test.sh
@@ -310,6 +310,12 @@ test_error() {
   compile_error 'noreturn should not return' 'void sub(void) __attribute__((noreturn));\nvoid sub(void){}\nint main(){ sub(); }'
   compile_error 'noreturn should be void' '#include <stdlib.h>\nint sub(void) __attribute__((noreturn));\nint sub(void){exit(0);}\nint main(){ sub(); }'
 
+  # Unused check.
+  compile_error 'unused local variable' 'int main(){ int x = 0; x = 1; return 0; }'
+  compile_error 'unused static variable' 'int main(){ static int x = 0; x = 1; return 0; }'
+  compile_error 'unused static global variable'    'static int s = 0; int g; int sub(){g=1; return 2;} int main(){ s = sub(); return g; }'
+  try_direct 'unused static can run w/o -Werror' 1 'static int s = 0; int g; int sub(){g=1; return 2;} int main(){ s = sub(); return g; } //-WNOERR'
+
   compile_error 'enum and global' 'enum Foo { BAR }; int BAR; int main(){}'
   compile_error 'global and enum' 'int BAR; enum Foo { BAR }; int main(){}'
   compile_error 'dup enum elem' 'enum Foo { BAR, BAR }; int main(){}'