The "overfull shares" problem is real as an arithmetic observation, but it does not prove a mathematical error in the Quran. It shows that Quranic inheritance verses give binding shares that sometimes require a legal rule for collision, and the jurists treated that collision by proportional reduction.
Why the objection sounds strong
The critic's best example is clear. Suppose a woman dies leaving a husband, two daughters, a mother, and a father. The husband is assigned one-quarter because there are children. The daughters are assigned two-thirds. Each parent is assigned one-sixth because there are children. Add them: 1/4 + 2/3 + 1/6 + 1/6 = 15/12. That is more than the estate.
So the objection says: if these are fixed divine fractions, they should always fit. Since they do not, later jurists must have invented "awl" - reducing everyone proportionally - to rescue the text.
What the verses actually give
Allah instructs you concerning your children: for the male, what is equal to the share of two females. But if there are only daughters, two or more, for them is two-thirds of what he left...
Quran 4:11
And for you is half of what your wives leave if they have no child. But if they have a child, for you is one-fourth of what they leave...
Quran 4:12
The verses assign legal entitlements to categories of heirs. They do not present themselves as a single spreadsheet formula saying, "In every possible combination, these fractions will sum to exactly one." Islamic law then asks: when valid entitlements meet and the estate is insufficient for their face values, how are they paid?
The answer of the overwhelming majority of jurists is "awl": the denominator is increased and all fixed-share heirs are reduced proportionally. In the example above, the estate is treated as 15 shares rather than 12. The husband receives 3/15, the daughters 8/15, the mother 2/15, and the father 2/15. No heir is erased; each bears the shortfall proportionally.
Why "awl" is not a desperate patch
This is not a trick unique to inheritance. When several valid claims exceed a limited fund, law often reduces claims proportionally. If an estate has debts greater than its assets, creditors are not paid by pretending the numbers add up; they are paid by a rule of abatement. That is not a denial of arithmetic. It is a rule for distributing shortage.
The Prophet (PBUH) taught that inheritance has both fixed shares and remainder rules:
Give the prescribed shares to those who are entitled to them, and whatever remains is for the closest male relative.
Sahih al-Bukhari and Sahih Muslim
This hadith shows that the Quranic shares function within a legal system: fixed heirs first, then residue where residue exists. In some cases there is no residue but an excess of fixed claims. The Companions and later jurists dealt with that by "awl". There was some early disagreement about method, most famously attributed to Ibn Abbas, but the proportional method became the settled view of the major schools because it preserves all named entitlements without arbitrary preference.
What this does and does not prove
It does prove that Quranic inheritance cannot be applied by merely adding isolated fractions in every family scenario and expecting them always to equal one. Muslim jurists never denied that.
It does not prove that the Quran made a mathematical mistake. A mistake would be saying that 1/4 + 2/3 + 1/6 + 1/6 = 1. The Quran does not say that. It gives heirs their rightful claims, while the legal tradition supplies the rule for what happens when claims overlap beyond the estate's capacity.
So the objection identifies a real feature of inheritance law, not a fatal flaw. The doctrine of "awl" is best understood as a principled legal mechanism for shortage, not as an embarrassment hidden under arithmetic.