diff --git a/ORCACDefs/math.h b/ORCACDefs/math.h
index 271e4b4..f007f5e 100644
--- a/ORCACDefs/math.h
+++ b/ORCACDefs/math.h
@@ -150,6 +150,9 @@ int             ilogbl(long double);
 double          ldexp(double, int);
 float           ldexpf(float, int);
 long double     ldexpl(long double, int);
+double          lgamma(double);
+float           lgammaf(float);
+long double     lgammal(long double);
 #if defined(__ORCAC_HAS_LONG_LONG__) || __STDC_VERSION__ >= 199901L
 long long       llrint(double);
 long long       llrintf(float);
diff --git a/ORCACDefs/tgmath.h b/ORCACDefs/tgmath.h
index b2e5805..2ee06d7 100644
--- a/ORCACDefs/tgmath.h
+++ b/ORCACDefs/tgmath.h
@@ -73,6 +73,7 @@
 #define hypot(x,y)      __tg_real_x_y(hypot,(x),(y))
 #define ilogb(x)        __tg_real_x(ilogb,(x))
 #define ldexp(x,n)      __tg_real_x_other(ldexp,(x),(n))
+#define lgamma(x)       __tg_real_x(lgamma,(x))
 #define llrint(x)       __tg_real_x(llrint,(x))
 #define llround(x)      __tg_real_x(llround,(x))
 #define log(x)          __tg_x(log,(x))
diff --git a/Tests/Conformance/c99math.c b/Tests/Conformance/c99math.c
index 63c8d9f..003aef8 100644
--- a/Tests/Conformance/c99math.c
+++ b/Tests/Conformance/c99math.c
@@ -365,6 +365,34 @@ int main(void) {
         expect_approx(erfcl(9.99L), 2.553157649309533e-45L);
         expect_approx(erfcl(105.0L), 4.300838032791244e-4791L);
 
+        expect_exact(lgamma(1.0), +0.0);
+        expect_exact(lgammaf(2.0), -0.0);
+        expect_pole_error(lgammal(0.0), +INFINITY);
+        expect_pole_error(lgammal(-0.0), +INFINITY);
+        expect_pole_error(lgammal(-1.0), +INFINITY);
+        expect_pole_error(lgammal(-2.0), +INFINITY);
+        expect_pole_error(lgammal(-3.0), +INFINITY);
+        expect_pole_error(lgammal(-1e50), +INFINITY);
+        expect_pole_error(lgammal(-LDBL_MAX), +INFINITY);
+        expect_exact(lgamma(-INFINITY), +INFINITY);
+        expect_exact(lgammaf(+INFINITY), +INFINITY);
+        expect_approx(lgammal(1e-50L), 1.151292546497022842e+02L);
+        expect_approx(lgammal(0.5L), 5.723649429247000870e-01L);
+        expect_approx(lgammal(0.99L), 5.854806764709776173e-03L);
+        expect_approx(lgammal(1.00000000001L), -5.772156625868682203e-12L);
+        expect_approx(lgammal(1.25L), -9.827183642181316143e-02L);
+        expect_approx(lgammal(1.9999999999L), -4.227843352103923846e-11L);
+        expect_approx(lgammal(2.125L), 5.775985153034387160e-02L);
+        expect_approx(lgammal(3.5L), 1.200973602347074225e+00L);
+        expect_approx(lgammal(1200.75L), 7.310783651998328589e+03L);
+        expect_approx(lgammal(1e4928L), 1.134613933827465713e+4932L);
+        expect_approx(lgammal(-0.00000000001L), 2.532843602294027468e+01L);
+        expect_approx(lgammal(-0.99L), 4.609530213895523164e+00L);
+        expect_approx(lgammal(-1.5L), 8.600470153764810144e-01L);
+        expect_approx(lgammal(-2.000000953674316L), 1.316979555107021760e+01L);
+        expect_approx(lgammal(-5.75L), -4.624612415302172588e+00L);
+        expect_approx(lgammal(-1000000000000.5L), -2.663102111595595344e+13L);
+
         expect_pole_error(tgamma(+0.0), +INFINITY);
         expect_pole_error(tgammaf(-0.0), -INFINITY);
         expect_domain_error(tgammal(-2.0));
diff --git a/cc.notes b/cc.notes
index 82ab2a0..785e7ef 100644
--- a/cc.notes
+++ b/cc.notes
@@ -1258,6 +1258,13 @@ int         ilogbl(long double x);
 
 These functions extract the binary exponent of x as an integer value, treating denormalized numbers as if they were normalized.  If x is 0, infinite, or NaN, they return the macro values FP_ILOGB0, INT_MAX, or FP_ILOGBNAN, respectively.
 
+#include <math.h>
+double      lgamma(double x);
+float       lgammaf(float x);
+long double lgammal(long double x);
+
+These functions compute the natural logarithm of the absolute value of the gamma function of x.
+
 #include <math.h>
 double      log1p(double x);
 float       log1pf(float x);