diff --git a/winsup/cygwin/math/ilogbl.S b/winsup/cygwin/math/ilogbl.S
index a4fe503ad..c75a7d0fd 100644
--- a/winsup/cygwin/math/ilogbl.S
+++ b/winsup/cygwin/math/ilogbl.S
@@ -23,6 +23,8 @@ __MINGW_USYMBOL(ilogbl):
 	andb    %ah, %dh
 	cmpb    $0x05, %dh
 	je      1f		/* Is +-Inf, jump.  */
+	cmpb	$0x01, %dh
+	je      1f		/* Is +-Inf, jump.  */
 	cmpb	$0x40, %dh
 	je	2f		/* Is +-Inf, jump.  */
 
@@ -53,6 +55,8 @@ __MINGW_USYMBOL(ilogbl):
 	andb    %ah, %dh
 	cmpb    $0x05, %dh
 	je      1f		/* Is +-Inf, jump.  */
+	cmpb	$0x01, %dh
+	je      1f		/* Is +-Inf, jump.  */
 	cmpb	$0x40, %dh
 	je	2f		/* Is +-Inf, jump.  */
 
diff --git a/winsup/cygwin/release/3.4.7 b/winsup/cygwin/release/3.4.7
index 1186e57f5..8ecfbc30a 100644
--- a/winsup/cygwin/release/3.4.7
+++ b/winsup/cygwin/release/3.4.7
@@ -15,3 +15,6 @@ Bug Fixes
 
 - Fix bug in cygheap allocation size computation after fork.  Addresses:
   https://cygwin.com/pipermail/cygwin-developers/2023-April/012620.html
+
+- Fix return value of ilogbl(NaN).
+  Addresses: https://cygwin.com/pipermail/cygwin/2023-April/253511.html