diff --git a/library/ecp_curves.c b/library/ecp_curves.c
index 962d5af..b167443 100644
--- a/library/ecp_curves.c
+++ b/library/ecp_curves.c
@@ -25,6 +25,8 @@
 #include "mbedtls/platform_util.h"
 #include "mbedtls/error.h"
 
+#include "ecp_invasive.h"
+
 #include <string.h>
 
 #if !defined(MBEDTLS_ECP_ALT)
@@ -1028,13 +1030,14 @@
     STORE32; i++;                               \
     cur = c > 0 ? c : 0; STORE32;               \
     cur = 0; while( ++i < MAX32 ) { STORE32; }  \
-    if( c < 0 ) fix_negative( N, c, bits );
+    if( c < 0 ) mbedtls_ecp_fix_negative( N, c, bits );
 
 /*
  * If the result is negative, we get it in the form
  * c * 2^(bits + 32) + N, with c negative and N positive shorter than 'bits'
  */
-static inline void fix_negative( mbedtls_mpi *N, signed char c, size_t bits )
+MBEDTLS_STATIC_TESTABLE
+void mbedtls_ecp_fix_negative( mbedtls_mpi *N, signed char c, size_t bits )
 {
     size_t i;
 
diff --git a/library/ecp_invasive.h b/library/ecp_invasive.h
index 7dd8ac2..870d963 100644
--- a/library/ecp_invasive.h
+++ b/library/ecp_invasive.h
@@ -31,6 +31,20 @@
 
 #if defined(MBEDTLS_TEST_HOOKS) && defined(MBEDTLS_ECP_C)
 
+#if defined(MBEDTLS_ECP_DP_SECP224R1_ENABLED) ||   \
+    defined(MBEDTLS_ECP_DP_SECP256R1_ENABLED) ||   \
+    defined(MBEDTLS_ECP_DP_SECP384R1_ENABLED)
+/* Preconditions:
+ *   - bits is a multiple of 64 or is 224
+ *   - c is -1 or -2
+ *   - 0 <= N < 2^bits
+ *   - N has room for bits+64 bits
+ *
+ * Set N to c * 2^bits + N.
+ */
+void mbedtls_ecp_fix_negative( mbedtls_mpi *N, signed char c, size_t bits );
+#endif
+
 #endif /* MBEDTLS_TEST_HOOKS && MBEDTLS_ECP_C */
 
 #endif /* MBEDTLS_ECP_INVASIVE_H */