diff --git a/src/arithmetic/bigint.rs b/src/arithmetic/bigint.rs
index f058c88d20..4f127b55dd 100644
--- a/src/arithmetic/bigint.rs
+++ b/src/arithmetic/bigint.rs
@@ -758,18 +758,6 @@ fn limbs_mont_square(r: &mut [Limb], m: &[Limb], n0: &N0, _cpu_features: cpu::Fe
     }
 }
 
-prefixed_extern! {
-    // `r` and/or 'a' and/or 'b' may alias.
-    fn bn_mul_mont(
-        r: *mut Limb,
-        a: *const Limb,
-        b: *const Limb,
-        n: *const Limb,
-        n0: &N0,
-        num_limbs: c::size_t,
-    );
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/src/arithmetic/montgomery.rs b/src/arithmetic/montgomery.rs
index 2f0fadf606..a155ec36bc 100644
--- a/src/arithmetic/montgomery.rs
+++ b/src/arithmetic/montgomery.rs
@@ -120,7 +120,7 @@ use crate::{bssl, c, limb::Limb};
 // TODO: Stop calling this from C and un-export it.
 #[allow(deprecated)]
 prefixed_export! {
-    unsafe fn bn_mul_mont(
+    pub(super) unsafe fn bn_mul_mont(
         r: *mut Limb,
         a: *const Limb,
         b: *const Limb,
@@ -218,6 +218,24 @@ prefixed_extern! {
     fn limbs_mul_add_limb(r: *mut Limb, a: *const Limb, b: Limb, num_limbs: c::size_t) -> Limb;
 }
 
+#[cfg(any(
+    target_arch = "aarch64",
+    target_arch = "arm",
+    target_arch = "x86_64",
+    target_arch = "x86"
+))]
+prefixed_extern! {
+    // `r` and/or 'a' and/or 'b' may alias.
+    pub(super) fn bn_mul_mont(
+        r: *mut Limb,
+        a: *const Limb,
+        b: *const Limb,
+        n: *const Limb,
+        n0: &N0,
+        num_limbs: c::size_t,
+    );
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;