diff --git a/wolfcrypt/src/sp_int.c b/wolfcrypt/src/sp_int.c
index 30d3d01a8..adc968c93 100644
--- a/wolfcrypt/src/sp_int.c
+++ b/wolfcrypt/src/sp_int.c
@@ -4768,11 +4768,17 @@ int sp_mod(sp_int* a, sp_int* m, sp_int* r)
             sp_int_word w;
             sp_int_word l;
             sp_int_word h;
+        #ifdef SP_WORD_OVERFLOW
+            sp_int_word o;
+        #endif
 
             w = (sp_int_word)a->dp[0] * b->dp[0];
             t->dp[0] = (sp_int_digit)w;
             l = (sp_int_digit)(w >> SP_WORD_SIZE);
             h = 0;
+        #ifdef SP_WORD_OVERFLOW
+            o = 0;
+        #endif
             for (k = 1; k <= (a->used - 1) + (b->used - 1); k++) {
                 i = k - (b->used - 1);
                 i &= ~(i >> (sizeof(i) * 8 - 1));
@@ -4781,11 +4787,21 @@ int sp_mod(sp_int* a, sp_int* m, sp_int* r)
                     w = (sp_int_word)a->dp[i] * b->dp[j];
                     l += (sp_int_digit)w;
                     h += (sp_int_digit)(w >> SP_WORD_SIZE);
+                #ifdef SP_WORD_OVERFLOW
+                    h += (sp_int_digit)(l >> SP_WORD_SIZE);
+                    l &= SP_MASK;
+                    o += (sp_int_digit)(h >> SP_WORD_SIZE);
+                    h &= SP_MASK;
+                #endif
                 }
                 t->dp[k] = (sp_int_digit)l;
                 l >>= SP_WORD_SIZE;
                 l += (sp_int_digit)h;
                 h >>= SP_WORD_SIZE;
+            #ifdef SP_WORD_OVERFLOW
+                h += o & SP_MASK;
+                o >>= SP_WORD_SIZE;
+            #endif
             }
             t->dp[k] = (sp_int_digit)l;
             t->dp[k+1] = (sp_int_digit)h;
@@ -9512,12 +9528,20 @@ int sp_mul_2d(sp_int* a, int e, sp_int* r)
     #endif
 
         if (err == MP_OKAY) {
-            sp_int_word w, l, h;
+            sp_int_word w;
+            sp_int_word l;
+            sp_int_word h;
+        #ifdef SP_WORD_OVERFLOW
+            sp_int_word o;
+        #endif
 
             w = (sp_int_word)a->dp[0] * a->dp[0];
             t->dp[0] = (sp_int_digit)w;
             l = (sp_int_digit)(w >> SP_WORD_SIZE);
             h = 0;
+        #ifdef SP_WORD_OVERFLOW
+            o = 0;
+        #endif
             for (k = 1; k <= (a->used - 1) * 2; k++) {
                 i = k / 2;
                 j = k - i;
@@ -9525,18 +9549,40 @@ int sp_mul_2d(sp_int* a, int e, sp_int* r)
                     w = (sp_int_word)a->dp[i] * a->dp[j];
                     l += (sp_int_digit)w;
                     h += (sp_int_digit)(w >> SP_WORD_SIZE);
+                #ifdef SP_WORD_OVERFLOW
+                    h += (sp_int_digit)(l >> SP_WORD_SIZE);
+                    l &= SP_MASK;
+                    o += (sp_int_digit)(h >> SP_WORD_SIZE);
+                    h &= SP_MASK;
+                #endif
                 }
                 for (++i, --j; (i < a->used) && (j >= 0); i++, j--) {
                     w = (sp_int_word)a->dp[i] * a->dp[j];
                     l += (sp_int_digit)w;
                     h += (sp_int_digit)(w >> SP_WORD_SIZE);
+                #ifdef SP_WORD_OVERFLOW
+                    h += (sp_int_digit)(l >> SP_WORD_SIZE);
+                    l &= SP_MASK;
+                    o += (sp_int_digit)(h >> SP_WORD_SIZE);
+                    h &= SP_MASK;
+                #endif
                     l += (sp_int_digit)w;
                     h += (sp_int_digit)(w >> SP_WORD_SIZE);
+                #ifdef SP_WORD_OVERFLOW
+                    h += (sp_int_digit)(l >> SP_WORD_SIZE);
+                    l &= SP_MASK;
+                    o += (sp_int_digit)(h >> SP_WORD_SIZE);
+                    h &= SP_MASK;
+                #endif
                 }
                 t->dp[k] = (sp_int_digit)l;
                 l >>= SP_WORD_SIZE;
                 l += (sp_int_digit)h;
                 h >>= SP_WORD_SIZE;
+            #ifdef SP_WORD_OVERFLOW
+                h += o & SP_MASK;
+                o >>= SP_WORD_SIZE;
+            #endif
             }
             t->dp[k] = (sp_int_digit)l;
             t->dp[k+1] = (sp_int_digit)h;
diff --git a/wolfcrypt/src/wolfmath.c b/wolfcrypt/src/wolfmath.c
index 40245ffd7..79a992d2b 100644
--- a/wolfcrypt/src/wolfmath.c
+++ b/wolfcrypt/src/wolfmath.c
@@ -99,7 +99,11 @@ int mp_cond_copy(mp_int* a, int copy, mp_int* b)
 {
     int err = MP_OKAY;
     int i;
+#if defined(SP_WORD_SIZE) && SP_WORD_SIZE == 8
+    unsigned int mask = (unsigned int)0 - copy;
+#else
     mp_digit mask = (mp_digit)0 - copy;
+#endif
 
     if (a == NULL || b == NULL)
         err = BAD_FUNC_ARG;
diff --git a/wolfssl/wolfcrypt/sp_int.h b/wolfssl/wolfcrypt/sp_int.h
index 96133133b..ccb52af78 100644
--- a/wolfssl/wolfcrypt/sp_int.h
+++ b/wolfssl/wolfcrypt/sp_int.h
@@ -376,6 +376,25 @@ typedef struct sp_ecc_ctx {
     #define SP_INT_MAX_BITS     (SP_INT_DIGITS * SP_WORD_SIZE)
 #endif
 
+#if SP_WORD_SIZE < 32
+    /* Maximum number of digits in a number to mul or sqr. */
+    #define SP_MUL_SQR_DIGITS       (SP_INT_MAX_BITS / 2 / SP_WORD_SIZE)
+    /* Maximum value of partial in mul/sqr. */
+    #define SP_MUL_SQR_MAX_PARTIAL  \
+                                 (SP_MUL_SQR_DIGITS * ((1 << SP_WORD_SIZE) - 1))
+    /* Maximim value in an sp_int_word. */
+    #define SP_INT_WORD_MAX         ((1 << (SP_WORD_SIZE * 2)) - 1)
+
+    #if SP_MUL_SQR_MAX_PARTIAL > SP_INT_WORD_MAX
+        /* The sum of the partials in the multiplicaiton/square can exceed the
+         * size of a word. This will overflow the word and loose data.
+         * Use an implementation that handles carry after every add and uses an
+         * extra temporary word for overflowing high word.
+         */
+        #define SP_WORD_OVERFLOW
+    #endif
+#endif
+
 
 /* For debugging only - format string for different digit sizes. */
 #if SP_WORD_SIZE == 64