diff --git a/lib/pocketsphinx/api/pocketsphinx.rb b/lib/pocketsphinx/api/pocketsphinx.rb
index 1a476ed..f474da9 100644
--- a/lib/pocketsphinx/api/pocketsphinx.rb
+++ b/lib/pocketsphinx/api/pocketsphinx.rb
@@ -6,6 +6,7 @@ module Pocketsphinx
 
       typedef :pointer, :decoder
       typedef :pointer, :configuration
+      typedef :pointer, :logmath
 
       # Allows expect(API::Pocketsphinx).to receive(:ps_init) in JRuby specs
       def self.ps_init(*args)
@@ -23,6 +24,9 @@ def self.ps_init(*args)
       attach_function :ps_get_in_speech, [:decoder], :uint8
       attach_function :ps_get_hyp, [:decoder, :pointer], :string
       attach_function :ps_get_prob, [:decoder], :int32
+      attach_function :ps_get_logmath, [:decoder], :logmath
+      attach_function :logmath_get_base, [:logmath], FFI::NativeType::FLOAT64
+      attach_function :logmath_exp, [:logmath, :int], FFI::NativeType::FLOAT64
       attach_function :ps_set_jsgf_string, [:decoder, :string, :string], :int
       attach_function :ps_unset_search, [:decoder, :string], :int
       attach_function :ps_get_search, [:decoder], :string
diff --git a/lib/pocketsphinx/decoder.rb b/lib/pocketsphinx/decoder.rb
index aa7aa69..a3adb60 100644
--- a/lib/pocketsphinx/decoder.rb
+++ b/lib/pocketsphinx/decoder.rb
@@ -117,9 +117,10 @@ def in_speech?
     # @return [Hypothesis] Hypothesis (behaves like a string)
     def hypothesis
       mp_path_score = FFI::MemoryPointer.new(:int32, 1)
+      logmath = ps_api.ps_get_logmath(ps_decoder)
 
       hypothesis = ps_api.ps_get_hyp(ps_decoder, mp_path_score)
-      posterior_prob = ps_api.ps_get_prob(ps_decoder)
+      posterior_prob = ps_api.logmath_exp(logmath, mp_path_score.get_int32(0))
 
       hypothesis.nil? ? nil : Hypothesis.new(
         hypothesis,
diff --git a/spec/decoder_spec.rb b/spec/decoder_spec.rb
index b9eaafe..21c203d 100644
--- a/spec/decoder_spec.rb
+++ b/spec/decoder_spec.rb
@@ -142,6 +142,9 @@
 
   describe '#hypothesis' do
     it 'calls libpocketsphinx' do
+      expect(ps_api)
+        .to receive(:ps_get_logmath)
+
       expect(ps_api)
         .to receive(:ps_get_hyp) do |ps_decoder, mp_path_score|
           expect(ps_decoder).to eq(subject.ps_decoder)
@@ -153,10 +156,10 @@
         end
 
       expect(ps_api)
-        .to receive(:ps_get_prob) do |ps_decoder|
-          expect(ps_decoder).to eq(subject.ps_decoder)
-          1
-        end
+        .to receive(:logmath_exp) do |logmath, mp_path_score_int|
+        expect(mp_path_score_int).to be_a(Integer)
+        1
+      end
 
       hypothesis = subject.hypothesis
 
diff --git a/spec/integration/decoder_spec.rb b/spec/integration/decoder_spec.rb
index d307f41..ac0c054 100644
--- a/spec/integration/decoder_spec.rb
+++ b/spec/integration/decoder_spec.rb
@@ -21,7 +21,7 @@
       expect(subject.hypothesis).to eq("go forward ten meters")
 
       expect(subject.hypothesis.path_score).to eq(-7636)
-      expect(subject.hypothesis.posterior_prob).to eq(-54501)
+      expect(subject.hypothesis.posterior_prob).to eq(0.4659446069409511)
     end
 
     # FIXME: This test illustrates a current issue discussed in: