More women have found their way into the C-suite in the past five years. But reaching parity with men in leadership roles is still far out of reach.

The percentage of C-suite executives who are women has risen to 21%, up from 17% five years ago, according to the latest Women in the Workplace survey, a joint effort of and McKinsey & Company. And 44% of companies now have three or more women in their C-suite, up from 29% in 2015.

Despite these improvements, gender disparity at the top shows no signs of disappearing. This stems from a promotion gap that occurs early on in women’s careers, the report showed.

“The biggest obstacle that women face is the first step up to manager, or [the] ‘broken rung.’ Women are less likely to be hired and promoted to manager,” researchers wrote.

The annual study, now in its fifth year, surveyed nearly 70,000 employees at 329 companies. It also pulled data directly from participating companies’ human resource files on promotions and diversity metrics, as well as from their hiring and promotion policies.

Overall, it found that only one in five C-suite executives is a woman. And only one in 25 is a woman of color.

That’s a direct result of the unequal rates at which men and women are made managers at lower levels, the study asserts. It found that for every 100 men promoted to or hired as managers, only 72 women are.

That helps explain why just 38% of managers in corporate America today are women.

“[T]here are significantly fewer women to advance to higher levels. So even as hiring and promotion rates improve for women at senior levels, women as a whole can never catch up,” the researchers wrote.

Conventional wisdom suggests that beyond gender bias, a big reason why more women aren’t managers and leaders is because they’re not as assertive in asking for raises and promotions, and that many step out of the workforce to care for family.

But the Lean In/McKinsey data suggest that may not be the case, at least not to the degree previously assumed.

The study found women reported asking for promotions and negotiating salaries at the same rate as men. And it found women don’t leave companies at higher rates than male employees. The vast majority of those who do plan to leave said they plan to keep working, the study showed.

How companies can narrow the gender gap in leadership

If companies commit to promoting or hiring women into managerial roles at the same rate as men, one million women would be added to the leadership ranks at corporations by 2024, the researchers project.

That commitment would require a multipronged approach.

The study recommends companies first become more conscious of the promotion gap at their organization and then set targets for getting women into first-level manager roles Currently only a third of companies set targets for hiring and promoting women into first-level manager roles.

And companies should require diversity in hiring and promotion to first-level manager positions and provide unconscious bias training to those who do entry-level performance reviews.

The researchers also recommend companies recognize that the work experience is not the same for all women.

“Women of color, lesbian and bisexual women, and women with disabilities are having distinct – and by and large worse – experiences than women overall,” the study said. “Most notably, Black women and women with disabilities face more barriers to advancement, get less support from managers, and receive less sponsorship than other groups of women.”

Companies should further commit to providing women with leadership training, sponsors and high-profile assignments to prepare them to assume managerial duties. And they should hold senior leaders accountable for increasing gender diversity targets in managerial jobs.

In other words, the study suggests, companies should treat gender diversity like it would any other business priority.

“It’s a fantastic signal that the commitment to gender diversity is rising. But companies are still lagging behind in treating diversity like it’s core to their business,” said LeanIn.Org CEO Rachel Thomas.

Alexis Krivkovich, a McKinsey Senior Partner and co-founder of the report, noted that there’s a key advantage for companies that fix the “broken rung” at the start of the pipeline. Prior McKinsey research has shown that companies with greater diversity throughout their ranks outperform financially.

And the pool of talent from which to choose first-time managers is already near parity since men and women enter the workforce in near-equal numbers.

“You have brand new fresh talent and you have tremendous ability to influence that quickly,” Krivkovich said.