diff --git a/src/maths/misc/Makefile.am b/src/maths/misc/Makefile.am
index f3b4087a0..62c8a4143 100644
--- a/src/maths/misc/Makefile.am
+++ b/src/maths/misc/Makefile.am
@@ -9,6 +9,7 @@ libmathmisc_la_SOURCES = \
 	bernoull.c 	\
 	erfc.c		\
 	equality.c	\
+	isinf.c		\
 	isnan.c		\
 	logb.c		\
 	scalb.c		\
diff --git a/src/maths/misc/isinf.c b/src/maths/misc/isinf.c
new file mode 100644
index 000000000..a0532e9d9
--- /dev/null
+++ b/src/maths/misc/isinf.c
@@ -0,0 +1,26 @@
+#include "ngspice.h"
+
+/* this is really ugly - but it is a emergency case */
+
+#ifndef HAVE_DECL_ISINF
+#ifndef HAVE_ISINF
+
+static int
+isinf(double x)
+{
+    volatile double a = x;
+
+    if (a > DBL_MAX)
+        return 1;
+    if (a < -DBL_MAX)
+        return -1;
+    return 0;
+}
+
+/*
+ * end isinf.c
+ */
+#else /* HAVE_ISINF */
+int Dummy_Symbol_5;
+#endif /* HAVE_ISINF */
+#endif /* HAVE_DECL_ISINF */