diff --git a/blas/testblas/common.go b/blas/testblas/common.go
index e7509105..8038bf57 100644
--- a/blas/testblas/common.go
+++ b/blas/testblas/common.go
@@ -254,22 +254,46 @@ func allPairs(x, y []int) [][2]int {
 	return p
 }
 
+func sameFloat64(a, b float64) bool {
+	return a == b || math.IsNaN(a) && math.IsNaN(b)
+}
+
+func sameComplex128(x, y complex128) bool {
+	return sameFloat64(real(x), real(y)) && sameFloat64(imag(x), imag(y))
+}
+
 func zsame(x, y []complex128) bool {
 	if len(x) != len(y) {
 		return false
 	}
 	for i, v := range x {
 		w := y[i]
-		if math.IsNaN(real(v)) && math.IsNaN(imag(v)) && math.IsNaN(real(w)) && math.IsNaN(imag(w)) {
+		if !sameComplex128(v, w) {
+			return false
+		}
+	}
+	return true
+}
+
+// zEqualApprox returns whether vectors x and y with stride inc
+// are approximately equal within tol. Elements at non-strided
+// positions must be same in both x and y.
+func zEqualApprox(x, y []complex128, inc int, tol float64) bool {
+	if len(x) != len(y) {
+		return false
+	}
+	if inc < 0 {
+		inc = -inc
+	}
+	for i, v := range x {
+		w := y[i]
+		if i%inc == 0 {
+			if cmplx.Abs(v-w) > tol {
+				return false
+			}
 			continue
 		}
-		if math.IsNaN(real(v)) && math.IsNaN(real(w)) && imag(v) == imag(w) {
-			continue
-		}
-		if math.IsNaN(imag(v)) && math.IsNaN(imag(w)) && real(v) == real(w) {
-			continue
-		}
-		if v != w {
+		if !sameComplex128(v, w) {
 			return false
 		}
 	}