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-rw-r--r--bits/mathdef.h4
1 files changed, 3 insertions, 1 deletions
diff --git a/bits/mathdef.h b/bits/mathdef.h
index d306e54366..0c30b01f52 100644
--- a/bits/mathdef.h
+++ b/bits/mathdef.h
@@ -20,7 +20,9 @@
 # error "Never use <bits/mathdef.h> directly; include <math.h> instead"
 #endif
 
-#if defined  __USE_ISOC99 && defined _MATH_H
+#if defined  __USE_ISOC99 && defined _MATH_H && !defined _MATH_H_MATHDEF
+# define _MATH_H_MATHDEF	1
+
 /* Normally, there is no long double type and the `float' and `double'
    expressions are evaluated as `double'.  */
 typedef double float_t;		/* `float' expressions are evaluated as