diff --git a/library/constant_time.c b/library/constant_time.c
index cb156bc9b..0c5c04c1f 100644
--- a/library/constant_time.c
+++ b/library/constant_time.c
@@ -92,3 +92,22 @@ int mbedtls_safer_memcmp( const void *a, const void *b, size_t n )
 
     return( diff );
 }
+
+/** Turn zero-or-nonzero into zero-or-all-bits-one, without branches.
+ *
+ * \param value     The value to analyze.
+ * \return          Zero if \p value is zero, otherwise all-bits-one.
+ */
+unsigned mbedtls_cf_uint_mask( unsigned value )
+{
+    /* MSVC has a warning about unary minus on unsigned, but this is
+     * well-defined and precisely what we want to do here */
+#if defined(_MSC_VER)
+#pragma warning( push )
+#pragma warning( disable : 4146 )
+#endif
+    return( - ( ( value | - value ) >> ( sizeof( value ) * 8 - 1 ) ) );
+#if defined(_MSC_VER)
+#pragma warning( pop )
+#endif
+}
diff --git a/library/constant_time.h b/library/constant_time.h
index e14232b8b..0d6c0fdfc 100644
--- a/library/constant_time.h
+++ b/library/constant_time.h
@@ -28,3 +28,6 @@ int mbedtls_constant_time_memcmp( const void *v1, const void *v2, size_t len );
 unsigned char mbedtls_nist_kw_safer_memcmp( const void *a, const void *b, size_t n );
 
 int mbedtls_safer_memcmp( const void *a, const void *b, size_t n );
+
+
+unsigned mbedtls_cf_uint_mask( unsigned value );
diff --git a/library/rsa.c b/library/rsa.c
index 06653a582..d5151a5e0 100644
--- a/library/rsa.c
+++ b/library/rsa.c
@@ -1479,25 +1479,6 @@ cleanup:
 #endif /* MBEDTLS_PKCS1_V21 */
 
 #if defined(MBEDTLS_PKCS1_V15)
-/** Turn zero-or-nonzero into zero-or-all-bits-one, without branches.
- *
- * \param value     The value to analyze.
- * \return          Zero if \p value is zero, otherwise all-bits-one.
- */
-static unsigned mbedtls_cf_uint_mask( unsigned value )
-{
-    /* MSVC has a warning about unary minus on unsigned, but this is
-     * well-defined and precisely what we want to do here */
-#if defined(_MSC_VER)
-#pragma warning( push )
-#pragma warning( disable : 4146 )
-#endif
-    return( - ( ( value | - value ) >> ( sizeof( value ) * 8 - 1 ) ) );
-#if defined(_MSC_VER)
-#pragma warning( pop )
-#endif
-}
-
 /** Check whether a size is out of bounds, without branches.
  *
  * This is equivalent to `size > max`, but is likely to be compiled to