diff --git a/library/bignum_core.c b/library/bignum_core.c
index ba6c0c13ae..a99b3be2bb 100644
--- a/library/bignum_core.c
+++ b/library/bignum_core.c
@@ -71,12 +71,10 @@ size_t mbedtls_mpi_core_bitlen(const mbedtls_mpi_uint *A, size_t A_limbs)
     int i;
     size_t j;
 
-    if (A_limbs != 0) {
-        for (i = (int) A_limbs - 1; i >= 0; i--) {
-            if (A[i] != 0) {
-                j = biL - mbedtls_mpi_core_clz(A[i]);
-                return (i * biL) + j;
-            }
+    for (i = ((int) A_limbs) - 1; i >= 0; i--) {
+        if (A[i] != 0) {
+            j = biL - mbedtls_mpi_core_clz(A[i]);
+            return (i * biL) + j;
         }
     }
 
diff --git a/tests/suites/test_suite_bignum_core.function b/tests/suites/test_suite_bignum_core.function
index 53aa002ce6..0cd1507b37 100644
--- a/tests/suites/test_suite_bignum_core.function
+++ b/tests/suites/test_suite_bignum_core.function
@@ -301,7 +301,11 @@ void mpi_core_bitlen(char *input_X, int nr_bits)
     mbedtls_mpi_uint *X = NULL;
     size_t limbs;
 
-    TEST_EQUAL(mbedtls_test_read_mpi_core(&X, &limbs, input_X), 0);
+    if (strlen(input_X) == 0) {
+        limbs = 0;
+    } else {
+        TEST_EQUAL(mbedtls_test_read_mpi_core(&X, &limbs, input_X), 0);
+    }
     TEST_EQUAL(mbedtls_mpi_core_bitlen(X, limbs), nr_bits);
 
 exit:
diff --git a/tests/suites/test_suite_bignum_core.misc.data b/tests/suites/test_suite_bignum_core.misc.data
index ba86029977..9e1b892fd7 100644
--- a/tests/suites/test_suite_bignum_core.misc.data
+++ b/tests/suites/test_suite_bignum_core.misc.data
@@ -155,6 +155,9 @@ mpi_core_bitlen:"10":5
 Test mbedtls_mpi_core_bitlen 0x0a
 mpi_core_bitlen:"a":4
 
+Test mbedtls_mpi_core_bitlen: 0 limbs
+mpi_core_bitlen:"":0
+
 Test mbedtls_mpi_core_bitlen: 0 (1 limb)
 mpi_core_bitlen:"0":0