diff --git a/options/ansi/musl-generic-math/__fpclassifyl.c b/options/ansi/musl-generic-math/__fpclassifyl.c
index 481c0b9499..fb62dd9fc4 100644
--- a/options/ansi/musl-generic-math/__fpclassifyl.c
+++ b/options/ansi/musl-generic-math/__fpclassifyl.c
@@ -13,10 +13,18 @@ int __fpclassifyl(long double x)
 	int msb = u.i.m>>63;
 	if (!e && !msb)
 		return u.i.m ? FP_SUBNORMAL : FP_ZERO;
+	if (e == 0x7fff) {
+		/* The x86 variant of 80-bit extended precision only admits
+		 * one representation of each infinity, with the mantissa msb
+		 * necessarily set. The version with it clear is invalid/nan.
+		 * The m68k variant, however, allows either, and tooling uses
+		 * the version with it clear. */
+		if (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ && !msb)
+			return FP_NAN;
+		return u.i.m << 1 ? FP_NAN : FP_INFINITE;
+	}
 	if (!msb)
 		return FP_NAN;
-	if (e == 0x7fff)
-		return u.i.m << 1 ? FP_NAN : FP_INFINITE;
 	return FP_NORMAL;
 }
 #elif LDBL_MANT_DIG == 113 && LDBL_MAX_EXP == 16384
diff --git a/options/ansi/musl-generic-math/libm.h b/options/ansi/musl-generic-math/libm.h
index 8120292ea8..2022cc5054 100644
--- a/options/ansi/musl-generic-math/libm.h
+++ b/options/ansi/musl-generic-math/libm.h
@@ -18,7 +18,7 @@
 #include <math.h>
 
 #if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
-#elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384 && __BYTE_ORDER == __LITTLE_ENDIAN
+#elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384 && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 union ldshape {
 	long double f;
 	struct {
@@ -26,7 +26,18 @@ union ldshape {
 		uint16_t se;
 	} i;
 };
-#elif LDBL_MANT_DIG == 113 && LDBL_MAX_EXP == 16384 && __BYTE_ORDER == __LITTLE_ENDIAN
+#elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384 && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+/* This is the m68k variant of 80-bit long double, and this definition only works
+ * on archs where the alignment requirement of uint64_t is <= 4. */
+union ldshape {
+	long double f;
+	struct {
+		uint16_t se;
+		uint16_t pad;
+		uint64_t m;
+	} i;
+};
+#elif LDBL_MANT_DIG == 113 && LDBL_MAX_EXP == 16384 && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 union ldshape {
 	long double f;
 	struct {
@@ -40,7 +51,7 @@ union ldshape {
 		uint64_t hi;
 	} i2;
 };
-#elif LDBL_MANT_DIG == 113 && LDBL_MAX_EXP == 16384 && __BYTE_ORDER == __BIG_ENDIAN
+#elif LDBL_MANT_DIG == 113 && LDBL_MAX_EXP == 16384 && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 union ldshape {
 	long double f;
 	struct {