diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3f7e7d0..59aba22 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 # v1.3.0
 * Improve supports for fractional seconds in input times by only rounding results at the end - [#42](https://github.com/Intrepidd/working_hours/issues/42) [#43](https://github.com/Intrepidd/working_hours/pull/43)
+* Increase code safety by always initializing an empty hash for each day of the week in the precompiled config (inspired by [#35](https://github.com/Intrepidd/working_hours/pull/35)
 
 # v1.2.0
 * Drop support for ruby 2.0, 2.1, 2.2 and 2.3
diff --git a/lib/working_hours/computation.rb b/lib/working_hours/computation.rb
index 07fb60e..bc71e43 100644
--- a/lib/working_hours/computation.rb
+++ b/lib/working_hours/computation.rb
@@ -80,7 +80,7 @@ def advance_to_working_time time, config: nil
         end
         # find first working range after time
         time_in_day = time.seconds_since_midnight
-        (config[:working_hours][time.wday] || {}).each do |from, to|
+        config[:working_hours][time.wday].each do |from, to|
           return time if time_in_day >= from and time_in_day < to
           return time + (from - time_in_day) if from >= time_in_day
         end
@@ -100,7 +100,7 @@ def advance_to_closing_time time, config: nil
         # find next working range after time
         time_in_day = time.seconds_since_midnight
         time = time.beginning_of_day
-        (config[:working_hours][time.wday] || {}).each do |from, to|
+        config[:working_hours][time.wday].each do |from, to|
           return time + to if time_in_day >= from and time_in_day < to
           return time + to if from >= time_in_day
         end
@@ -131,7 +131,7 @@ def return_to_exact_working_time time, config: nil
         end
         # find last working range before time
         time_in_day = time.seconds_since_midnight
-        (config[:working_hours][time.wday] || {}).reverse_each do |from, to|
+        config[:working_hours][time.wday].reverse_each do |from, to|
           # round is used to suppress miliseconds hack from `end_of_day`
           return time if time_in_day > from and time_in_day <= to
           return (time - (time_in_day - to)) if to <= time_in_day
diff --git a/lib/working_hours/config.rb b/lib/working_hours/config.rb
index 462e378..81dea66 100644
--- a/lib/working_hours/config.rb
+++ b/lib/working_hours/config.rb
@@ -44,9 +44,8 @@ def precompiled
           validate_working_hours! config[:working_hours]
           validate_holidays! config[:holidays]
           validate_time_zone! config[:time_zone]
-          compiled = {working_hours: []}
+          compiled = { working_hours: Array.new(7) { Hash.new } }
           working_hours.each do |day, hours|
-            compiled[:working_hours][DAYS_OF_WEEK.index(day)] = {}
             hours.each do |start, finish|
               compiled[:working_hours][DAYS_OF_WEEK.index(day)][compile_time(start)] = compile_time(finish)
             end
diff --git a/spec/working_hours/config_spec.rb b/spec/working_hours/config_spec.rb
index e2ba767..79a0c62 100644
--- a/spec/working_hours/config_spec.rb
+++ b/spec/working_hours/config_spec.rb
@@ -266,16 +266,23 @@
 
     it 'computes an optimized version' do
       expect(subject).to eq({
-          :working_hours => [nil, {32400=>61200}, {32400=>61200}, {32400=>61200}, {32400=>61200}, {32400=>61200}],
+          :working_hours => [{}, {32400=>61200}, {32400=>61200}, {32400=>61200}, {32400=>61200}, {32400=>61200}, {}],
           :holidays => Set.new([]),
           :time_zone => ActiveSupport::TimeZone['UTC']
         })
     end
 
+    it 'includes default values for each days so computation does not fail' do
+      WorkingHours::Config.working_hours = {:mon => {'08:00' => '14:00'}}
+      expect(subject[:working_hours]).to eq([{}, {28800=>50400}, {}, {}, {}, {}, {}])
+      expect(WorkingHours.working_time_between(Time.utc(2014, 4, 14, 0), Time.utc(2014, 4, 21, 0))).to eq(3600*6)
+      expect(WorkingHours.add_seconds(Time.utc(2014, 4, 14, 0), 3600*7)).to eq(Time.utc(2014, 4, 21, 9))
+    end
+
     it 'supports seconds' do
       WorkingHours::Config.working_hours = {:mon => {'20:32:59' => '22:59:59'}}
       expect(subject).to eq({
-        :working_hours => [nil, {73979 => 82799}],
+        :working_hours => [{}, {73979 => 82799}, {}, {}, {}, {}, {}],
         :holidays => Set.new([]),
         :time_zone => ActiveSupport::TimeZone['UTC']
       })
@@ -284,7 +291,7 @@
     it 'supports 24:00 (converts to 23:59:59.999999)' do
       WorkingHours::Config.working_hours = {:mon => {'20:00' => '24:00'}}
       expect(subject).to eq({
-        :working_hours => [nil, {72000 => 86399.999999}],
+        :working_hours => [{}, {72000 => 86399.999999}, {}, {}, {}, {}, {}],
         :holidays => Set.new([]),
         :time_zone => ActiveSupport::TimeZone['UTC']
       })
@@ -296,9 +303,9 @@
       }.to change {
         WorkingHours::Config.precompiled[:working_hours]
       }.from(
-        [nil, {32400=>61200}, {32400=>61200}, {32400=>61200}, {32400=>61200}, {32400=>61200}]
+        [{}, {32400=>61200}, {32400=>61200}, {32400=>61200}, {32400=>61200}, {32400=>61200}, {}]
       ).to(
-        [nil, {28800=>50400}]
+        [{}, {28800=>50400}, {}, {}, {}, {}, {}]
       )
     end