diff --git a/SConstruct b/SConstruct
index 3c51288..50b9bf7 100644
--- a/SConstruct
+++ b/SConstruct
@@ -1,14 +1,10 @@
 double_conversion_sources = ['src/' + x for x in SConscript('src/SConscript')]
 double_conversion_test_sources = ['test/cctest/' + x for x in SConscript('test/cctest/SConscript')]
-test = double_conversion_sources + double_conversion_test_sources
-print(test)
 env = Environment(CPPPATH='#/src', LIBS=['m', 'stdc++'])
 debug = ARGUMENTS.get('debug', 0)
 optimize = ARGUMENTS.get('optimize', 0)
 if int(debug):
   env.Append(CCFLAGS = '-g -Wall -Werror')
 if int(optimize):
-  env.Append(CCFLAGS = '-O3')
-print double_conversion_sources
-print double_conversion_test_sources
+  env.Append(CCFLAGS = '-O3 -Wall -Werror')
 env.Program('run_tests', double_conversion_sources + double_conversion_test_sources)
diff --git a/src/bignum-dtoa.cc b/src/bignum-dtoa.cc
index b6c2e85..f1ad7a5 100644
--- a/src/bignum-dtoa.cc
+++ b/src/bignum-dtoa.cc
@@ -192,13 +192,13 @@
     delta_plus = delta_minus;
   }
   *length = 0;
-  while (true) {
+  for (;;) {
     uint16_t digit;
     digit = numerator->DivideModuloIntBignum(*denominator);
     ASSERT(digit <= 9);  // digit is a uint16_t and therefore always positive.
     // digit = numerator / denominator (integer division).
     // numerator = numerator % denominator.
-    buffer[(*length)++] = digit + '0';
+    buffer[(*length)++] = static_cast<char>(digit + '0');
 
     // Can we stop already?
     // If the remainder of the division is less than the distance to the lower
@@ -282,7 +282,7 @@
 // exponent (decimal_point), when rounding upwards.
 static void GenerateCountedDigits(int count, int* decimal_point,
                                   Bignum* numerator, Bignum* denominator,
-                                  Vector<char>(buffer), int* length) {
+                                  Vector<char> buffer, int* length) {
   ASSERT(count >= 0);
   for (int i = 0; i < count - 1; ++i) {
     uint16_t digit;
@@ -290,7 +290,7 @@
     ASSERT(digit <= 9);  // digit is a uint16_t and therefore always positive.
     // digit = numerator / denominator (integer division).
     // numerator = numerator % denominator.
-    buffer[i] = digit + '0';
+    buffer[i] = static_cast<char>(digit + '0');
     // Prepare for next iteration.
     numerator->Times10();
   }
@@ -300,7 +300,8 @@
   if (Bignum::PlusCompare(*numerator, *numerator, *denominator) >= 0) {
     digit++;
   }
-  buffer[count - 1] = digit + '0';
+  ASSERT(digit <= 10);
+  buffer[count - 1] = static_cast<char>(digit + '0');
   // Correct bad digits (in case we had a sequence of '9's). Propagate the
   // carry until we hat a non-'9' or til we reach the first digit.
   for (int i = count - 1; i > 0; --i) {
diff --git a/src/bignum.cc b/src/bignum.cc
index dc8a2a6..a20df23 100644
--- a/src/bignum.cc
+++ b/src/bignum.cc
@@ -122,9 +122,8 @@
 static int HexCharValue(char c) {
   if ('0' <= c && c <= '9') return c - '0';
   if ('a' <= c && c <= 'f') return 10 + c - 'a';
-  if ('A' <= c && c <= 'F') return 10 + c - 'A';
-  UNREACHABLE();
-  return 0;  // To make compiler happy.
+  ASSERT('A' <= c && c <= 'F');
+  return 10 + c - 'A';
 }
 
 
@@ -505,9 +504,10 @@
     // is big. This function is implemented for doubleToString where
     // the result should be small (less than 10).
     ASSERT(other.bigits_[other.used_digits_ - 1] >= ((1 << kBigitSize) / 16));
+    ASSERT(bigits_[used_digits_ - 1] < 0x10000);
     // Remove the multiples of the first digit.
     // Example this = 23 and other equals 9. -> Remove 2 multiples.
-    result += bigits_[used_digits_ - 1];
+    result += static_cast<uint16_t>(bigits_[used_digits_ - 1]);
     SubtractTimes(other, bigits_[used_digits_ - 1]);
   }
 
@@ -523,13 +523,15 @@
     // Shortcut for easy (and common) case.
     int quotient = this_bigit / other_bigit;
     bigits_[used_digits_ - 1] = this_bigit - other_bigit * quotient;
-    result += quotient;
+    ASSERT(quotient < 0x10000);
+    result += static_cast<uint16_t>(quotient);
     Clamp();
     return result;
   }
 
   int division_estimate = this_bigit / (other_bigit + 1);
-  result += division_estimate;
+  ASSERT(division_estimate < 0x10000);
+  result += static_cast<uint16_t>(division_estimate);
   SubtractTimes(other, division_estimate);
 
   if (other_bigit * (division_estimate + 1) > this_bigit) {
@@ -560,8 +562,8 @@
 
 static char HexCharOfValue(int value) {
   ASSERT(0 <= value && value <= 16);
-  if (value < 10) return value + '0';
-  return value - 10 + 'A';
+  if (value < 10) return static_cast<char>(value + '0');
+  return static_cast<char>(value - 10 + 'A');
 }
 
 
diff --git a/src/cached-powers.cc b/src/cached-powers.cc
index c676429..d1359ff 100644
--- a/src/cached-powers.cc
+++ b/src/cached-powers.cc
@@ -152,6 +152,7 @@
   ASSERT(0 <= index && index < kCachedPowersLength);
   CachedPower cached_power = kCachedPowers[index];
   ASSERT(min_exponent <= cached_power.binary_exponent);
+  (void) max_exponent;  // Mark variable as used.
   ASSERT(cached_power.binary_exponent <= max_exponent);
   *decimal_exponent = cached_power.decimal_exponent;
   *power = DiyFp(cached_power.significand, cached_power.binary_exponent);
diff --git a/src/double-conversion.cc b/src/double-conversion.cc
index 1a9767b..f276ba6 100644
--- a/src/double-conversion.cc
+++ b/src/double-conversion.cc
@@ -552,7 +552,7 @@
       exponent = overflow_bits_count;
 
       bool zero_tail = true;
-      while (true) {
+      for (;;) {
         ++(*current);
         if (*current == end || !isDigit(**current, radix)) break;
         zero_tail = zero_tail && **current == '0';
diff --git a/src/fast-dtoa.cc b/src/fast-dtoa.cc
index 1a0f823..6135038 100644
--- a/src/fast-dtoa.cc
+++ b/src/fast-dtoa.cc
@@ -248,10 +248,7 @@
   // Note: kPowersOf10[i] == 10^(i-1).
   exponent_plus_one_guess++;
   // We don't have any guarantees that 2^number_bits <= number.
-  // TODO(floitsch): can we change the 'while' into an 'if'? We definitely see
-  // number < (2^number_bits - 1), but I haven't encountered
-  // number < (2^number_bits - 2) yet.
-  while (number < kSmallPowersOfTen[exponent_plus_one_guess]) {
+  if (number < kSmallPowersOfTen[exponent_plus_one_guess]) {
     exponent_plus_one_guess--;
   }
   *power = kSmallPowersOfTen[exponent_plus_one_guess];
@@ -350,7 +347,8 @@
   // that is smaller than integrals.
   while (*kappa > 0) {
     int digit = integrals / divisor;
-    buffer[*length] = '0' + digit;
+    ASSERT(digit <= 9);
+    buffer[*length] = static_cast<char>('0' + digit);
     (*length)++;
     integrals %= divisor;
     (*kappa)--;
@@ -379,13 +377,14 @@
   ASSERT(one.e() >= -60);
   ASSERT(fractionals < one.f());
   ASSERT(UINT64_2PART_C(0xFFFFFFFF, FFFFFFFF) / 10 >= one.f());
-  while (true) {
+  for (;;) {
     fractionals *= 10;
     unit *= 10;
     unsafe_interval.set_f(unsafe_interval.f() * 10);
     // Integer division by one.
     int digit = static_cast<int>(fractionals >> -one.e());
-    buffer[*length] = '0' + digit;
+    ASSERT(digit <= 9);
+    buffer[*length] = static_cast<char>('0' + digit);
     (*length)++;
     fractionals &= one.f() - 1;  // Modulo by one.
     (*kappa)--;
@@ -459,7 +458,8 @@
   // that is smaller than 'integrals'.
   while (*kappa > 0) {
     int digit = integrals / divisor;
-    buffer[*length] = '0' + digit;
+    ASSERT(digit <= 9);
+    buffer[*length] = static_cast<char>('0' + digit);
     (*length)++;
     requested_digits--;
     integrals %= divisor;
@@ -492,7 +492,8 @@
     w_error *= 10;
     // Integer division by one.
     int digit = static_cast<int>(fractionals >> -one.e());
-    buffer[*length] = '0' + digit;
+    ASSERT(digit <= 9);
+    buffer[*length] = static_cast<char>('0' + digit);
     (*length)++;
     requested_digits--;
     fractionals &= one.f() - 1;  // Modulo by one.
diff --git a/src/fixed-dtoa.cc b/src/fixed-dtoa.cc
index d56b144..aef65fd 100644
--- a/src/fixed-dtoa.cc
+++ b/src/fixed-dtoa.cc
@@ -133,7 +133,7 @@
   while (number != 0) {
     int digit = number % 10;
     number /= 10;
-    buffer[(*length) + number_length] = '0' + digit;
+    buffer[(*length) + number_length] = static_cast<char>('0' + digit);
     number_length++;
   }
   // Exchange the digits.
@@ -150,7 +150,7 @@
 }
 
 
-static void FillDigits64FixedLength(uint64_t number, int requested_length,
+static void FillDigits64FixedLength(uint64_t number,
                                     Vector<char> buffer, int* length) {
   const uint32_t kTen7 = 10000000;
   // For efficiency cut the number into 3 uint32_t parts, and print those.
@@ -253,7 +253,8 @@
       fractionals *= 5;
       point--;
       int digit = static_cast<int>(fractionals >> point);
-      buffer[*length] = '0' + digit;
+      ASSERT(digit <= 9);
+      buffer[*length] = static_cast<char>('0' + digit);
       (*length)++;
       fractionals -= static_cast<uint64_t>(digit) << point;
     }
@@ -274,7 +275,8 @@
       fractionals128.Multiply(5);
       point--;
       int digit = fractionals128.DivModPowerOf2(point);
-      buffer[*length] = '0' + digit;
+      ASSERT(digit <= 9);
+      buffer[*length] = static_cast<char>('0' + digit);
       (*length)++;
     }
     if (fractionals128.BitAt(point - 1) == 1) {
@@ -358,7 +360,7 @@
       remainder = (dividend % divisor) << exponent;
     }
     FillDigits32(quotient, buffer, length);
-    FillDigits64FixedLength(remainder, divisor_power, buffer, length);
+    FillDigits64FixedLength(remainder, buffer, length);
     *decimal_point = *length;
   } else if (exponent >= 0) {
     // 0 <= exponent <= 11
diff --git a/src/ieee.h b/src/ieee.h
index 839dc47..661141d 100644
--- a/src/ieee.h
+++ b/src/ieee.h
@@ -256,6 +256,8 @@
     return (significand & kSignificandMask) |
         (biased_exponent << kPhysicalSignificandSize);
   }
+
+  DISALLOW_COPY_AND_ASSIGN(Double);
 };
 
 class Single {
@@ -391,6 +393,8 @@
   static const uint32_t kNaN = 0x7FC00000;
 
   const uint32_t d32_;
+
+  DISALLOW_COPY_AND_ASSIGN(Single);
 };
 
 }  // namespace double_conversion
diff --git a/src/strtod.cc b/src/strtod.cc
index 9758989..68d0217 100644
--- a/src/strtod.cc
+++ b/src/strtod.cc
@@ -137,6 +137,7 @@
   Vector<const char> right_trimmed = TrimTrailingZeros(left_trimmed);
   exponent += left_trimmed.length() - right_trimmed.length();
   if (right_trimmed.length() > kMaxSignificantDecimalDigits) {
+    (void) space_size;  // Mark variable as used.
     ASSERT(space_size >= kMaxSignificantDecimalDigits);
     CutToMaxSignificantDigits(right_trimmed, exponent,
                               buffer_copy_space, updated_exponent);
@@ -515,6 +516,7 @@
     double double_next2 = Double(double_next).NextDouble();
     f4 = static_cast<float>(double_next2);
   }
+  (void) f2;  // Mark variable as used.
   ASSERT(f1 <= f2 && f2 <= f3 && f3 <= f4);
 
   // If the guess doesn't lie near a single-precision boundary we can simply
diff --git a/src/utils.h b/src/utils.h
index c76f77d..f598e98 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -34,9 +34,7 @@
 #include <assert.h>
 #ifndef ASSERT
 #define ASSERT(condition)         \
-  do {                            \
-    assert(condition);            \
-  } while (false && (condition))
+    assert(condition);
 #endif
 #ifndef UNIMPLEMENTED
 #define UNIMPLEMENTED() (abort())