diff --git a/spec/std/math_spec.cr b/spec/std/math_spec.cr
index fc64e698421d..5855939e33f6 100644
--- a/spec/std/math_spec.cr
+++ b/spec/std/math_spec.cr
@@ -192,11 +192,15 @@ describe "Math" do
     it "gamma" do
       Math.gamma(3.2_f32).should be_close(2.4239654799353683, 1e-6)
       Math.gamma(3.2).should be_close(2.4239654799353683, 1e-7)
+      Math.gamma(5).should eq 24
+      Math.gamma(5_i8).should eq 24
     end
 
     it "lgamma" do
       Math.lgamma(2.96_f32).should be_close(0.6565534110944214, 1e-7)
       Math.lgamma(2.96).should be_close(0.6565534110944214, 1e-7)
+      Math.lgamma(3).should be_close(0.6931471805599454, 1e-7)
+      Math.lgamma(3_i8).should be_close(0.6931471805599454, 1e-7)
     end
   end
 
diff --git a/src/math/math.cr b/src/math/math.cr
index 904faf16feb7..49a7d45764e6 100644
--- a/src/math/math.cr
+++ b/src/math/math.cr
@@ -62,7 +62,7 @@ module Math
 
   # ditto
   def gamma(value)
-    LibM.tgamma(value)
+    gamma(value.to_f)
   end
 
   # Calculates the logarithmic gamma of *value*.
@@ -89,7 +89,7 @@ module Math
 
   # ditto
   def lgamma(value)
-    LibM.gamma(value.to_f)
+    lgamma(value.to_f)
   end
 
   {% for name in %w(atan2 copysign hypot) %}