diff --git a/src/big/big_decimal.cr b/src/big/big_decimal.cr
index d0aaa92aa0d9..21909c05c7a0 100644
--- a/src/big/big_decimal.cr
+++ b/src/big/big_decimal.cr
@@ -1,3 +1,5 @@
+require "big"
+
 # A `BigDecimal` represents arbitrary precision decimals.
 #
 # It is internally represented by a pair of `BigInt` and `UInt64`: value and scale.
diff --git a/src/big/big_float.cr b/src/big/big_float.cr
index 29d0da0969f7..d7f7161abae6 100644
--- a/src/big/big_float.cr
+++ b/src/big/big_float.cr
@@ -1,4 +1,5 @@
 require "c/string"
+require "big"
 
 # A `BigFloat` can represent arbitrarily large floats.
 #
diff --git a/src/big/big_int.cr b/src/big/big_int.cr
index ca8e86d60359..8070d319e6ed 100644
--- a/src/big/big_int.cr
+++ b/src/big/big_int.cr
@@ -1,4 +1,5 @@
 require "c/string"
+require "big"
 
 # A `BigInt` can represent arbitrarily large integers.
 #
diff --git a/src/big/big_rational.cr b/src/big/big_rational.cr
index 7eae41d64e22..089f900287e4 100644
--- a/src/big/big_rational.cr
+++ b/src/big/big_rational.cr
@@ -1,3 +1,5 @@
+require "big"
+
 # Rational numbers are represented as the quotient of arbitrarily large
 # numerators and denominators. Rationals are canonicalized such that the
 # denominator and the numerator have no common factors, and that the