diff --git a/ex-2/fancier.c b/ex-2/fancier.c
index c26557d..35946c6 100644
--- a/ex-2/fancier.c
+++ b/ex-2/fancier.c
@@ -85,6 +85,10 @@ char* mpq_dec_str(mpq_t z, size_t mantissa_size) {
 }
 
 
+/* printf() like function with special conversion %q, which
+ * prints the deciamal expansion of mpq_t rational numbers.
+ * The second argument is the number of digits shown.
+ */
 void mpq_fprintf(FILE *fp, size_t digits, char* fmt, ...) {
   va_list args;
   va_start(args, fmt);
@@ -243,6 +247,26 @@ void mpq_log_ui(mpq_t rop, size_t x, size_t digits) {
   fprintf(stderr, "[mpq_log_ui] binary digits: %ld\n", m);
   fprintf(stderr, "[mpq_log_ui] a=%g\n", mpq_get_d(a));
 
+  // calculate log(2)*(m-1)
+  mpq_t log2; mpq_init(log2);
+  mpq_log2(log2, digits);
+
+  mpz_mul_ui(mpq_numref(log2), mpq_numref(log2), m-1);
+  mpq_canonicalize(log2);
+
+  /* When x is a power of two a=1 and y=0.
+   * The series for log(1+y/1-y) is not defined for y=0
+   * so this case must be handled separately.
+   */
+  if (mpq_cmp_ui(a, 1, 1) == 0) {
+    mpq_set(rop, log2);
+
+    // free memory
+    mpq_clears(a, log2, NULL);
+    mpz_clears(xz, power, NULL);
+    return;
+  }
+
   /* calculate y = (a-1)/(a+1) */
   mpq_t y, temp; mpq_inits(y, temp, NULL);
 
@@ -366,13 +390,6 @@ void mpq_log_ui(mpq_t rop, size_t x, size_t digits) {
   mpq_fprintf(stderr, d+2, "[mpq_log_ui] lower bound: %q...\n", low);
   mpq_fprintf(stderr, d,   "[mpq_log_ui] series: %q...\n", sum);
 
-  // calculate log(2)*(m-1)
-  mpq_t log2; mpq_init(log2);
-  mpq_log2(log2, digits);
-
-  mpz_mul_ui(mpq_numref(log2), mpq_numref(log2), m-1);
-  mpq_canonicalize(log2);
-
   // series += log(2)*(m-1)
   mpq_add(sum, sum, log2);
   mpq_set(rop, sum);