diff --git a/lib/libm_dbl/round.c b/lib/libm_dbl/round.c
new file mode 100644
index 0000000000..130d58d257
--- /dev/null
+++ b/lib/libm_dbl/round.c
@@ -0,0 +1,35 @@
+#include "libm.h"
+
+#if FLT_EVAL_METHOD==0 || FLT_EVAL_METHOD==1
+#define EPS DBL_EPSILON
+#elif FLT_EVAL_METHOD==2
+#define EPS LDBL_EPSILON
+#endif
+static const double_t toint = 1/EPS;
+
+double round(double x)
+{
+	union {double f; uint64_t i;} u = {x};
+	int e = u.i >> 52 & 0x7ff;
+	double_t y;
+
+	if (e >= 0x3ff+52)
+		return x;
+	if (u.i >> 63)
+		x = -x;
+	if (e < 0x3ff-1) {
+		/* raise inexact if x!=0 */
+		FORCE_EVAL(x + toint);
+		return 0*u.f;
+	}
+	y = x + toint - toint - x;
+	if (y > 0.5)
+		y = y + x - 1;
+	else if (y <= -0.5)
+		y = y + x + 1;
+	else
+		y = y + x;
+	if (u.i >> 63)
+		y = -y;
+	return y;
+}
diff --git a/ports/stm32/Makefile b/ports/stm32/Makefile
index fe8f0b8711..e7d2e2abc2 100644
--- a/ports/stm32/Makefile
+++ b/ports/stm32/Makefile
@@ -191,6 +191,7 @@ LIBM_SRC_C = $(addprefix lib/libm_dbl/,\
 	nearbyint.c \
 	pow.c \
 	rint.c \
+	round.c \
 	scalbn.c \
 	sin.c \
 	sinh.c \