diff --git a/std/range/primitives.d b/std/range/primitives.d
index 6862c5cd8..316c5c6ab 100644
--- a/std/range/primitives.d
+++ b/std/range/primitives.d
@@ -1750,6 +1750,20 @@ if (isInputRange!Range && !isInfinite!Range)
     else
     {
         size_t result;
+        static if (autodecodeStrings && isNarrowString!Range)
+        {
+            import std.utf : codeUnitLimit;
+            result = range.length;
+            foreach (const i, const c; range)
+            {
+                if (c >= codeUnitLimit!Range)
+                {
+                    result = i;
+                    break;
+                }
+            }
+            range = range[result .. $];
+        }
         for ( ; !range.empty ; range.popFront() )
             ++result;
         return result;
@@ -1766,6 +1780,20 @@ if (isInputRange!Range)
     else
     {
         size_t result;
+        static if (autodecodeStrings && isNarrowString!Range)
+        {
+            import std.utf : codeUnitLimit;
+            result = upTo > range.length ? range.length : upTo;
+            foreach (const i, const c; range[0 .. result])
+            {
+                if (c >= codeUnitLimit!Range)
+                {
+                    result = i;
+                    break;
+                }
+            }
+            range = range[result .. $];
+        }
         for ( ; result < upTo && !range.empty ; range.popFront() )
             ++result;
         return result;
diff --git a/std/utf.d b/std/utf.d
index 1849726b0..4a093cc7c 100644
--- a/std/utf.d
+++ b/std/utf.d
@@ -1410,7 +1410,8 @@ do
     assert(str.decodeBack(i) == 'å' && i == 2 && str.empty);
 }
 
-// Gives the maximum value that a code unit for the given range type can hold.
+// For the given range, code unit values less than this
+// are guaranteed to be valid single-codepoint encodings.
 package template codeUnitLimit(S)
 if (isSomeChar!(ElementEncodingType!S))
 {