diff --git a/crypto.go b/crypto.go
index b63623e..17f0d5b 100644
--- a/crypto.go
+++ b/crypto.go
@@ -95,6 +95,7 @@ func htpasswd(username string, password string, hashAlgorithm HashAlgorithm) str
 }
 
 func randBytes(count int) (string, error) {
+	count = clampInt(count, maxAllocSize)
 	buf := make([]byte, count)
 	if _, err := rand.Read(buf); err != nil {
 		return "", err
diff --git a/functions.go b/functions.go
index cda47d2..19aa504 100644
--- a/functions.go
+++ b/functions.go
@@ -125,7 +125,7 @@ var genericMap = map[string]interface{}{
 	"untitle":    untitle,
 	"substr":     substring,
 	// Switch order so that "foo" | repeat 5
-	"repeat": func(count int, str string) string { return strings.Repeat(str, count) },
+	"repeat": func(count int, str string) string { return strings.Repeat(str, clampInt(count, maxAllocSize)) },
 	// Deprecated: Use trimAll.
 	"trimall": func(a, b string) string { return strings.Trim(b, a) },
 	// Switch order so that "$foo" | trimall "$"
diff --git a/limits.go b/limits.go
new file mode 100644
index 0000000..f74955d
--- /dev/null
+++ b/limits.go
@@ -0,0 +1,16 @@
+package sprig
+
+// maxAllocSize is the maximum number of elements or bytes that template
+// functions are allowed to allocate in a single call.  This prevents
+// denial-of-service when user-controlled input is passed as a size parameter.
+const maxAllocSize = 1 << 20 // 1 MiB / ~1 million elements
+
+func clampInt(n, max int) int {
+	if n < 0 {
+		n = 0
+	}
+	if n > max {
+		return max
+	}
+	return n
+}
diff --git a/numeric.go b/numeric.go
index f68e418..2dc8e7e 100644
--- a/numeric.go
+++ b/numeric.go
@@ -65,6 +65,11 @@ func minf(a interface{}, i ...interface{}) float64 {
 }
 
 func until(count int) []int {
+	if count > maxAllocSize {
+		count = maxAllocSize
+	} else if count < -maxAllocSize {
+		count = -maxAllocSize
+	}
 	step := 1
 	if count < 0 {
 		step = -1
diff --git a/strings.go b/strings.go
index e0ae628..448775b 100644
--- a/strings.go
+++ b/strings.go
@@ -56,22 +56,26 @@ func initials(s string) string {
 }
 
 func randAlphaNumeric(count int) string {
+	count = clampInt(count, maxAllocSize)
 	// It is not possible, it appears, to actually generate an error here.
 	r, _ := util.CryptoRandomAlphaNumeric(count)
 	return r
 }
 
 func randAlpha(count int) string {
+	count = clampInt(count, maxAllocSize)
 	r, _ := util.CryptoRandomAlphabetic(count)
 	return r
 }
 
 func randAscii(count int) string {
+	count = clampInt(count, maxAllocSize)
 	r, _ := util.CryptoRandomAscii(count)
 	return r
 }
 
 func randNumeric(count int) string {
+	count = clampInt(count, maxAllocSize)
 	r, _ := util.CryptoRandomNumeric(count)
 	return r
 }
@@ -107,6 +111,7 @@ func cat(v ...interface{}) string {
 }
 
 func indent(spaces int, v string) string {
+	spaces = clampInt(spaces, maxAllocSize)
 	pad := strings.Repeat(" ", spaces)
 	return pad + strings.Replace(v, "\n", "\n"+pad, -1)
 }