diff --git a/reactos/lib/sdk/crt/float/fpclass.c b/reactos/lib/sdk/crt/float/fpclass.c
index 6d61b4252f5..b2ca7e3026a 100644
--- a/reactos/lib/sdk/crt/float/fpclass.c
+++ b/reactos/lib/sdk/crt/float/fpclass.c
@@ -1,8 +1,8 @@
 /*
  * COPYRIGHT:   See COPYING in the top level directory
  * PROJECT:     ReactOS system libraries
- * FILE:        lib/crt/??????
- * PURPOSE:     Unknown
+ * FILE:        lib/sdk/crt/float/fpclass.c
+ * PURPOSE:     Floating-point classes
  * PROGRAMER:   Unknown
  * UPDATE HISTORY:
  *              25/11/05: Added license header
@@ -55,32 +55,28 @@ fpclass_t _fpclass(double __d)
 	d.__d = &__d;
 
 	if ( d.d->exponent == 0 ) {
-		if ( d.d->mantissah == 0 &&  d.d->mantissal == 0 ) {
-			if ( d.d->sign ==0 )
-				return FP_NZERO;
-			else
+		if ( d.d->mantissah == 0 && d.d->mantissal == 0 ) {
+			if ( d.d->sign == 0 )
 				return FP_PZERO;
-		} else {
-			if ( d.d->sign ==0 )
-				return FP_NDENORM;
 			else
+				return FP_NZERO;
+		} else {
+			if ( d.d->sign == 0 )
 				return FP_PDENORM;
+			else
+				return FP_NDENORM;
 		}
 	}
-	if (d.d->exponent == 0x7ff ) {
-		if ( d.d->mantissah == 0 &&  d.d->mantissal == 0 ) {
-			if ( d.d->sign ==0 )
-				return FP_NINF;
-			else
+	else if (d.d->exponent == 0x7ff ) {
+		if ( d.d->mantissah == 0 && d.d->mantissal == 0 ) {
+			if ( d.d->sign == 0 )
 				return FP_PINF;
+			else
+				return FP_NINF;
 		}
-		else if ( d.d->mantissah == 0 &&  d.d->mantissal != 0 ) {
+		else if ( (d.d->mantissah & 0x80000) != 0 ) {
 			return FP_QNAN;
 		}
-		else if ( d.d->mantissah == 0 &&  d.d->mantissal != 0 ) {
-			return FP_SNAN;
-		}
-
 	}
-	return 0;
+	return FP_SNAN;
 }
diff --git a/reactos/lib/sdk/crt/float/isnan.c b/reactos/lib/sdk/crt/float/isnan.c
index fb328d30d97..ab0684e0ac0 100644
--- a/reactos/lib/sdk/crt/float/isnan.c
+++ b/reactos/lib/sdk/crt/float/isnan.c
@@ -50,7 +50,7 @@ int _isnanl(long double __x)
      exponent and a nonzero mantissa.  */
 
 	return (( x.x->exponent == 0x7fff)
-	  && ( (x.x->mantissah & 0x80000000) != 0)
+	  && ( (x.x->mantissah & 0x80000) != 0)
 	  && ( (x.x->mantissah & (unsigned int)0x7fffffff) != 0  || x.x->mantissal != 0 ));
 }
 
@@ -91,7 +91,7 @@ int _isinfl(long double __x)
      maximum possible value and a zero mantissa.  */
 
 
-	if ( x.x->exponent == 0x7fff  && ( (x.x->mantissah == 0x80000000 )   && x.x->mantissal == 0 ))
+	if ( x.x->exponent == 0x7fff  && ( (x.x->mantissah == 0x80000 )   && x.x->mantissal == 0 ))
 		return x.x->sign ? -1 : 1;
 	return 0;
 }