diff --git a/run.c b/run.c
index 26e8c4f..41f1bbe 100644
--- a/run.c
+++ b/run.c
@@ -25,6 +25,7 @@ THIS SOFTWARE.
 #define DEBUG
 #include <stdio.h>
 #include <ctype.h>
+#include <errno.h>
 #include <wchar.h>
 #include <wctype.h>
 #include <fcntl.h>
@@ -1072,8 +1073,10 @@ Cell *arith(Node **a, int n)	/* a[0] + a[1], etc.  also -a[0] */
 	case POWER:
 		if (j >= 0 && modf(j, &v) == 0.0)	/* pos integer exponent */
 			i = ipow(i, (int) j);
-		else
+               else {
+			errno = 0;
 			i = errcheck(pow(i, j), "pow");
+               }
 		break;
 	default:	/* can't happen */
 		FATAL("illegal arithmetic operator %d", n);
@@ -1166,8 +1169,10 @@ Cell *assign(Node **a, int n)	/* a[0] = a[1], a[0] += a[1], etc. */
 	case POWEQ:
 		if (yf >= 0 && modf(yf, &v) == 0.0)	/* pos integer exponent */
 			xf = ipow(xf, (int) yf);
-		else
+               else {
+			errno = 0;
 			xf = errcheck(pow(xf, yf), "pow");
+               }
 		break;
 	default:
 		FATAL("illegal assignment operator %d", n);
@@ -1589,13 +1594,19 @@ Cell *bltin(Node **a, int n)	/* builtin functions. a[0] is type, a[1] is arg lis
 			u = strlen(getsval(x));
 		break;
 	case FLOG:
-		u = errcheck(log(getfval(x)), "log"); break;
+		errno = 0;
+		u = errcheck(log(getfval(x)), "log");
+		break;
 	case FINT:
 		modf(getfval(x), &u); break;
 	case FEXP:
-		u = errcheck(exp(getfval(x)), "exp"); break;
+		errno = 0;
+		u = errcheck(exp(getfval(x)), "exp");
+		break;
 	case FSQRT:
-		u = errcheck(sqrt(getfval(x)), "sqrt"); break;
+		errno = 0;
+		u = errcheck(sqrt(getfval(x)), "sqrt");
+		break;
 	case FSIN:
 		u = sin(getfval(x)); break;
 	case FCOS: