4 files changed, 14 insertions, 0 deletions
diff --git a/libraries/base/GHC/Bits.hs b/libraries/base/GHC/Bits.hs
index e74e8bb6d0..4c3bef2f44 100644
--- a/libraries/base/GHC/Bits.hs
+++ b/libraries/base/GHC/Bits.hs
@@ -583,6 +583,7 @@ instance Bits Natural where
      | otherwise = naturalShiftR x (fromIntegral (negate i))
    testBit x i   = naturalTestBit x (fromIntegral i)
    zeroBits      = naturalZero
+   setBit x i    = naturalSetBit x (fromIntegral i)
    clearBit x i  = x `xor` (bit i .&. x)
 
    bit (I# i)  = naturalBit# (int2Word# i)
diff --git a/libraries/ghc-bignum/changelog.md b/libraries/ghc-bignum/changelog.md
index 015721d40b..d57a6d8a68 100644
--- a/libraries/ghc-bignum/changelog.md
+++ b/libraries/ghc-bignum/changelog.md
@@ -3,6 +3,7 @@
 ## 1.3
 
 - Expose backendName
+- Add `naturalSetBit[#]` (#21173)
 
 ## 1.2
 
diff --git a/libraries/ghc-bignum/src/GHC/Num/BigNat.hs b/libraries/ghc-bignum/src/GHC/Num/BigNat.hs
index 5fa81b7e5b..bab3a97190 100644
--- a/libraries/ghc-bignum/src/GHC/Num/BigNat.hs
+++ b/libraries/ghc-bignum/src/GHC/Num/BigNat.hs
@@ -1045,6 +1045,7 @@ bigNatClearBit# a n
 
 -- | BigNat set bit
 bigNatSetBit# :: BigNat# -> Word# -> BigNat#
+{-# NOINLINE bigNatSetBit# #-}
 bigNatSetBit# a n
    -- check the current bit value
    | isTrue# (bigNatTestBit# a n) = a
diff --git a/libraries/ghc-bignum/src/GHC/Num/Natural.hs b/libraries/ghc-bignum/src/GHC/Num/Natural.hs
index 72b646501d..8fe737bf07 100644
--- a/libraries/ghc-bignum/src/GHC/Num/Natural.hs
+++ b/libraries/ghc-bignum/src/GHC/Num/Natural.hs
@@ -421,6 +421,17 @@ naturalBit# i
 naturalBit :: Word -> Natural
 naturalBit (W# i) = naturalBit# i
 
+-- | @since 1.3
+naturalSetBit# :: Natural -> Word# -> Natural
+naturalSetBit# (NS n) i
+  | isTrue# (i `ltWord#` WORD_SIZE_IN_BITS##) = NS (n `or#` (1## `uncheckedShiftL#` word2Int# i))
+  | True                                      = NB (bigNatSetBit# (bigNatFromWord# n) i)
+naturalSetBit# (NB n) i                       = NB (bigNatSetBit# n i)
+
+-- | @since 1.3
+naturalSetBit :: Natural -> Word -> Natural
+naturalSetBit !n (W# i) = naturalSetBit# n i
+
 -- | Compute greatest common divisor.
 naturalGcd :: Natural -> Natural -> Natural
 {-# NOINLINE naturalGcd #-}