diff --git a/test/test_test.c b/test/test_test.c
index 0094c1c6436e0a66d5fd0de5b267a866b616cf54..7a5079a1402816af77214586d8de48e2e00e5585 100644
--- a/test/test_test.c
+++ b/test/test_test.c
@@ -306,6 +306,9 @@ static int test_bignum(void)
         | !TEST(0, TEST_BN_gt_zero(a))
         | !TEST(1, TEST_BN_even(a))
         | !TEST(0, TEST_BN_odd(a))
+        | !TEST(1, TEST_BN_eq(b, c))
+        | !TEST(0, TEST_BN_eq(a, b))
+        | !TEST(1, TEST_BN_ne(NULL, c))
         | !TEST(1, TEST_int_eq(BN_dec2bn(&b, "1"), 1))
         | !TEST(1, TEST_BN_eq_word(b, 1))
         | !TEST(1, TEST_BN_eq_one(b))
@@ -374,6 +377,46 @@ static int test_long_output(void)
            & TEST(0, TEST_mem_eq(r, strlen(r), s, strlen(s)));
 }
 
+static int test_long_bignum(void)
+{
+    int r;
+    BIGNUM *a = NULL, *b = NULL, *c = NULL, *d = NULL;
+    const char as[] = "1234567890123456789012345678901234567890123456789012"
+                      "1234567890123456789012345678901234567890123456789012"
+                      "1234567890123456789012345678901234567890123456789012"
+                      "1234567890123456789012345678901234567890123456789012"
+                      "1234567890123456789012345678901234567890123456789012"
+                      "1234567890123456789012345678901234567890123456789012"
+                      "FFFFFF";
+    const char bs[] = "1234567890123456789012345678901234567890123456789012"
+                      "1234567890123456789012345678901234567890123456789013"
+                      "987657";
+    const char cs[] = "-"        /* 64 characters plus sign */
+                      "123456789012345678901234567890"
+                      "123456789012345678901234567890"
+                      "ABCD";
+    const char ds[] = "-"        /* 63 characters plus sign */
+                      "23456789A123456789B123456789C"
+                      "123456789D123456789E123456789F"
+                      "ABCD";
+
+    r = TEST_true(BN_hex2bn(&a, as))
+        && TEST_true(BN_hex2bn(&b, bs))
+        && TEST_true(BN_hex2bn(&c, cs))
+        && TEST_true(BN_hex2bn(&d, ds))
+        && (TEST(0, TEST_BN_eq(a, b))
+            & TEST(0, TEST_BN_eq(b, a))
+            & TEST(0, TEST_BN_eq(b, NULL))
+            & TEST(0, TEST_BN_eq(NULL, a))
+            & TEST(1, TEST_BN_ne(a, NULL))
+            & TEST(0, TEST_BN_eq(c, d)));
+    BN_free(a);
+    BN_free(b);
+    BN_free(c);
+    BN_free(d);
+    return r;
+}
+
 static int test_messages(void)
 {
     TEST_info("This is an %s message.", "info");
@@ -452,6 +495,7 @@ void register_tests(void)
     ADD_TEST(test_memory_overflow);
     ADD_TEST(test_bignum);
     ADD_TEST(test_long_output);
+    ADD_TEST(test_long_bignum);
     ADD_TEST(test_messages);
     ADD_TEST(test_single_eval);
 }
diff --git a/test/testutil/tests.c b/test/testutil/tests.c
index a6c9a99df0fb767576065c4f7cc5cc505774d230..ef020f7899ac7bf55d357d538f93802f191197ab 100644
--- a/test/testutil/tests.c
+++ b/test/testutil/tests.c
@@ -16,11 +16,9 @@
 #include "../../e_os.h"
 
 /* The size of memory buffers to display on failure */
-#define MEM_BUFFER_SIZE     (33)
+#define MEM_BUFFER_SIZE     (2000)
 #define MAX_STRING_WIDTH    (80)
-
-/* Special representation of -0 */
-static char BN_minus_zero[] = "-0";
+#define BN_OUTPUT_SIZE      (8)
 
 /* Output a failed test first line */
 static void test_fail_message_prefix(const char *prefix, const char *file,
@@ -184,13 +182,195 @@ fin:
     test_flush_stderr();
 }
 
-static char *convertBN(const BIGNUM *b)
+static void hex_convert_memory(const unsigned char *m, size_t n, char *b,
+                               size_t width)
+{
+    size_t i;
+
+    for (i = 0; i < n; i++) {
+        const unsigned char c = *m++;
+
+        *b++ = "0123456789abcdef"[c >> 4];
+        *b++ = "0123456789abcdef"[c & 15];
+        if (i % width == width - 1 && i != n - 1)
+            *b++ = ' ';
+    }
+    *b = '\0';
+}
+
+static const int bn_bytes = (MAX_STRING_WIDTH - 9) / (BN_OUTPUT_SIZE * 2 + 1)
+                            * BN_OUTPUT_SIZE;
+static const int bn_chars = (MAX_STRING_WIDTH - 9) / (BN_OUTPUT_SIZE * 2 + 1)
+                            * (BN_OUTPUT_SIZE * 2 + 1) - 1;
+
+static void test_bignum_header_line(void)
+{
+    test_printf_stderr("%*s#  %*s\n", subtest_level(), "", bn_chars + 6,
+                       "bit position");
+}
+
+static void test_bignum_zero_print(const BIGNUM *bn, char sep)
+{
+    const char *v = "NULL", *suf = "";
+    if (bn != NULL) {
+        suf = ":    0";
+        v = BN_is_negative(bn) ? "-0" : "0";
+    }
+    test_printf_stderr("%*s# %c%*s%s\n", subtest_level(), "", sep, bn_chars,
+                       v, suf);
+}
+
+static int convert_bn_memory(const unsigned char *in, size_t bytes,
+                             char *out, int *lz, const BIGNUM *bn)
 {
-    if (b == NULL)
-        return NULL;
-    if (BN_is_zero(b) && BN_is_negative(b))
-        return BN_minus_zero;
-    return BN_bn2hex(b);
+    int n = bytes * 2, i;
+    char *p = out, *q = NULL;
+
+    if (bn != NULL && !BN_is_zero(bn)) {
+        hex_convert_memory(in, bytes, out, BN_OUTPUT_SIZE);
+        if (*lz) {
+            for (; *p == '0' || *p == ' '; p++)
+                if (*p == '0') {
+                    q = p;
+                    *p = ' ';
+                    n--;
+                }
+            if (*p == '\0') {
+                /*
+                 * in[bytes] is defined because we're converting a non-zero
+                 * number and we've not seen a non-zero yet.
+                 */
+                if ((in[bytes] & 0xf0) != 0 && BN_is_negative(bn)) {
+                    *lz = 0;
+                    *q = '-';
+                    n++;
+                }
+            } else {
+                *lz = 0;
+                if (BN_is_negative(bn)) {
+                    /*
+                     * This is valid because we always convert more digits than
+                     * the number holds.
+                     */
+                    *q = '-';
+                    n++;
+                }
+            }
+        }
+       return n;
+    }
+
+    for (i = 0; i < n; i++) {
+        *p++ = ' ';
+        if (i % (2 * BN_OUTPUT_SIZE) == 2 * BN_OUTPUT_SIZE - 1 && i != n - 1)
+            *p++ = ' ';
+    }
+    *p = '\0';
+    if (bn == NULL)
+        q = "NULL";
+    else
+        q = BN_is_negative(bn) ? "-0" : "0";
+    strcpy(p - strlen(q), q);
+    return 0;
+}
+
+static void test_fail_bignum_common(const char *prefix, const char *file,
+                                    int line, const char *type,
+                                    const char *left, const char *right,
+                                    const char *op,
+                                    const BIGNUM *bn1, const BIGNUM *bn2)
+{
+    const int indent = subtest_level();
+    const size_t bytes = bn_bytes;
+    char b1[MAX_STRING_WIDTH + 1], b2[MAX_STRING_WIDTH + 1];
+    char *p, bdiff[MAX_STRING_WIDTH + 1];
+    size_t l1, l2, n1, n2, i, len;
+    unsigned int cnt, diff, real_diff;
+    unsigned char *m1 = NULL, *m2 = NULL;
+    int lz1 = 1, lz2 = 1;
+    unsigned char buffer[MEM_BUFFER_SIZE * 2], *bufp = buffer;
+
+    l1 = bn1 == NULL ? 0 : (BN_num_bytes(bn1) + (BN_is_negative(bn1) ? 1 : 0));
+    l2 = bn2 == NULL ? 0 : (BN_num_bytes(bn2) + (BN_is_negative(bn2) ? 1 : 0));
+    if (l1 == 0 && l2 == 0) {
+        if ((bn1 == NULL) == (bn2 == NULL)) {
+            test_bignum_header_line();
+            test_bignum_zero_print(bn1, ' ');
+        } else {
+            test_diff_header(left, right);
+            test_bignum_header_line();
+            test_bignum_zero_print(bn1, '-');
+            test_bignum_zero_print(bn2, '+');
+        }
+        goto fin;
+    }
+
+    if (l1 != l2 || bn1 == NULL || bn2 == NULL || BN_cmp(bn1, bn2) != 0)
+        test_diff_header(left, right);
+    test_bignum_header_line();
+
+    len = ((l1 > l2 ? l1 : l2) + bytes - 1) / bytes * bytes;
+
+    if (len > MEM_BUFFER_SIZE && (bufp = OPENSSL_malloc(len * 2)) == NULL) {
+        bufp = buffer;
+        len = MEM_BUFFER_SIZE;
+        test_printf_stderr("%*s# WARNING: these BIGNUMs have been truncated",
+                           indent, "");
+    }
+
+    if (bn1 != NULL) {
+        m1 = bufp;
+        BN_bn2binpad(bn1, m1, len);
+    }
+    if (bn2 != NULL) {
+        m2 = bufp + len;
+        BN_bn2binpad(bn2, m2, len);
+    }
+
+    while (len > 0) {
+        cnt = 8 * (len - bytes);
+        n1 = convert_bn_memory(m1, bytes, b1, &lz1, bn1);
+        n2 = convert_bn_memory(m2, bytes, b2, &lz2, bn2);
+
+        diff = real_diff = 0;
+        i = 0;
+        p = bdiff;
+        for (i=0; b1[i] != '\0'; i++)
+            if (b1[i] == b2[i] || b1[i] == ' ' || b2[i] == ' ') {
+                *p++ = ' ';
+                diff |= b1[i] != b2[i];
+            } else {
+                *p++ = '^';
+                real_diff = diff = 1;
+            }
+        *p++ = '\0';
+        if (!diff) {
+            test_printf_stderr("%*s#  %s:% 5d\n", indent, "",
+                               n2 > n1 ? b2 : b1, cnt);
+        } else {
+            if (cnt == 0 && bn1 == NULL)
+                test_printf_stderr("%*s# -%s\n", indent, "", b1);
+            else if (cnt == 0 || n1 > 0)
+                test_printf_stderr("%*s# -%s:% 5d\n", indent, "", b1, cnt);
+            if (cnt == 0 && bn2 == NULL)
+                test_printf_stderr("%*s# +%s\n", indent, "", b2);
+            else if (cnt == 0 || n2 > 0)
+                test_printf_stderr("%*s# +%s:% 5d\n", indent, "", b2, cnt);
+            if (real_diff && (cnt == 0 || (n1 > 0 && n2 > 0))
+                    && bn1 != NULL && bn2 != NULL)
+                test_printf_stderr("%*s#  %s\n", indent, "", bdiff);
+        }
+        if (m1 != NULL)
+            m1 += bytes;
+        if (m2 != NULL)
+            m2 += bytes;
+        len -= bytes;
+    }
+fin:
+    test_printf_stderr("\n");
+    test_flush_stderr();
+    if (bufp != buffer)
+        OPENSSL_free(bufp);
 }
 
 static void test_fail_bignum_message(const char *prefix, const char *file,
@@ -199,16 +379,8 @@ static void test_fail_bignum_message(const char *prefix, const char *file,
                                      const char *op,
                                      const BIGNUM *bn1, const BIGNUM *bn2)
 {
-    char *s1 = convertBN(bn1), *s2 = convertBN(bn2);
-    size_t l1 = s1 != NULL ? strlen(s1) : 0;
-    size_t l2 = s2 != NULL ? strlen(s2) : 0;
-
-    test_fail_string_message(prefix, file, line, type, left, right, op,
-                             s1, l1, s2, l2);
-    if (s1 != BN_minus_zero)
-        OPENSSL_free(s1);
-    if (s2 != BN_minus_zero)
-        OPENSSL_free(s2);
+    test_fail_message_prefix(prefix, file, line, type, left, right, op);
+    test_fail_bignum_common(prefix, file, line, type, left, right, op, bn1, bn2);
 }
 
 static void test_fail_bignum_mono_message(const char *prefix, const char *file,
@@ -216,35 +388,16 @@ static void test_fail_bignum_mono_message(const char *prefix, const char *file,
                                           const char *left, const char *right,
                                           const char *op, const BIGNUM *bn)
 {
-    char *s = convertBN(bn);
-    size_t l = s != NULL ? strlen(s) : 0;
-
-    test_fail_string_message(prefix, file, line, type, left, right, op,
-                             s, l, s, l);
-    if (s != BN_minus_zero)
-        OPENSSL_free(s);
-}
-
-static void hex_convert_memory(const char *m, size_t n, char *b)
-{
-    size_t i;
-
-    for (i = 0; i < n; i++) {
-        const unsigned char c = *m++;
-
-        *b++ = "0123456789abcdef"[c >> 4];
-        *b++ = "0123456789abcdef"[c & 15];
-        if ((i % 8) == 7 && i != n - 1)
-            *b++ = ' ';
-    }
-    *b = '\0';
+    test_fail_message_prefix(prefix, file, line, type, left, right, op);
+    test_fail_bignum_common(prefix, file, line, type, left, right, op, bn, bn);
 }
 
 static void test_fail_memory_message(const char *prefix, const char *file,
                                      int line, const char *type,
                                      const char *left, const char *right,
-                                     const char *op, const char *m1, size_t l1,
-                                     const char *m2, size_t l2)
+                                     const char *op,
+                                     const unsigned char *m1, size_t l1,
+                                     const unsigned char *m2, size_t l2)
 {
     const int indent = subtest_level();
     const size_t bytes = (MAX_STRING_WIDTH - 9) / 17 * 8;
@@ -279,11 +432,11 @@ static void test_fail_memory_message(const char *prefix, const char *file,
         n1 = n2 = 0;
         if (l1 > 0) {
             n1 = l1 > bytes ? bytes : l1;
-            hex_convert_memory(m1, n1, b1);
+            hex_convert_memory(m1, n1, b1, 8);
         }
         if (l2 > 0) {
             n2 = l2 > bytes ? bytes : l2;
-            hex_convert_memory(m2, n2, b2);
+            hex_convert_memory(m2, n2, b2, 8);
         }
 
         diff = n1 != n2;
@@ -607,8 +760,7 @@ int test_BN_odd(const char *file, int line, const char *s, const BIGNUM *a)
 {
     if (a != NULL && BN_is_odd(a))
         return 1;
-    test_fail_bignum_mono_message(NULL, file, line, "BIGNUM", "ODD(", ")", s,
-                                  a);
+    test_fail_bignum_mono_message(NULL, file, line, "BIGNUM", "ODD(", ")", s, a);
     return 0;
 }