diff --git a/libc/math.h b/libc/math.h
index 0087f694c..e49e3f612 100644
--- a/libc/math.h
+++ b/libc/math.h
@@ -64,6 +64,8 @@
 #define FP_ZERO      2
 #define FP_SUBNORMAL 3
 #define FP_NORMAL    4
+#define FP_ILOGB0    (-2147483647-1)
+#define FP_ILOGBNAN  (-2147483647-1)
 
 #if !(__ASSEMBLER__ + __LINKER__ + 0)
 COSMOPOLITAN_C_START_
diff --git a/test/libc/tinymath/logb_test.c b/test/libc/tinymath/logb_test.c
index 0a6c54e1d..73abda775 100644
--- a/test/libc/tinymath/logb_test.c
+++ b/test/libc/tinymath/logb_test.c
@@ -49,3 +49,14 @@ TEST(logb, yolo) {
   EXPECT_EQ(2, (int)logbl(4));
   EXPECT_EQ(63, (int)logbl(1e19));
 }
+
+TEST(ilogb, NANandZero) {
+  EXPECT_EQ(FP_ILOGB0, ilogb(0.0));
+  EXPECT_EQ(FP_ILOGBNAN, ilogb(NAN));
+  EXPECT_EQ(FP_ILOGB0, (int)ilogb(0));
+  EXPECT_EQ(FP_ILOGBNAN, (int)ilogb(NAN));
+  EXPECT_EQ(FP_ILOGB0, ilogbf(0));
+  EXPECT_EQ(FP_ILOGBNAN, ilogbf(NAN));
+  EXPECT_EQ(FP_ILOGB0, ilogbl(0));
+  EXPECT_EQ(FP_ILOGBNAN, ilogbl(NAN));
+}