diff --git a/src/Runic.jl b/src/Runic.jl
index ef3a708..7b5c1df 100644
--- a/src/Runic.jl
+++ b/src/Runic.jl
@@ -69,10 +69,11 @@ function next_sibling_kind(ctx::Context)::Union{JuliaSyntax.Kind, Nothing}
 end
 
 # Read the bytes of the current node from the output io
-function node_bytes(ctx, node)
-    pos = mark(ctx.fmt_io)
+function read_bytes(ctx, node)
+    pos = position(ctx.fmt_io)
     bytes = read(ctx.fmt_io, JuliaSyntax.span(node))
-    reset(ctx.fmt_io)
+    @assert length(bytes) == JuliaSyntax.span(node)
+    seek(ctx.fmt_io, pos)
     @assert position(ctx.fmt_io) == pos
     return bytes
 end
diff --git a/src/runestone.jl b/src/runestone.jl
index 4b79b25..a1e0f64 100644
--- a/src/runestone.jl
+++ b/src/runestone.jl
@@ -5,7 +5,7 @@
 function trim_trailing_whitespace(ctx::Context, node::JuliaSyntax.GreenNode)
     JuliaSyntax.kind(node) === K"NewlineWs" || return nothing
     @assert !JuliaSyntax.haschildren(node)
-    str = String(node_bytes(ctx, node))
+    str = String(read_bytes(ctx, node))
     str′ = replace(str, r"\h*(\r\n|\r|\n)" => '\n')
     # If the next sibling is also a NewlineWs we can trim trailing
     # whitespace from this node too
@@ -39,7 +39,7 @@ function format_hex_literals(ctx::Context, node::JuliaSyntax.GreenNode)
     end
     # Insert leading zeros
     i = findfirst(x -> x > span, target_spans)::Int
-    bytes = node_bytes(ctx, node)
+    bytes = read_bytes(ctx, node)
     while length(bytes) < target_spans[i]
         insert!(bytes, 3, '0')
     end
@@ -57,7 +57,7 @@ function format_oct_literals(ctx::Context, node::JuliaSyntax.GreenNode)
     span = JuliaSyntax.span(node)
     @assert span > 2 # 0o prefix + something more
     # Padding depends on the value of the literal...
-    str = String(node_bytes(ctx, node))
+    str = String(read_bytes(ctx, node))
     n = tryparse(UInt128, str)
     if n === nothing
         # Do nothing: BigInt oct literal
@@ -77,7 +77,7 @@ function format_oct_literals(ctx::Context, node::JuliaSyntax.GreenNode)
         return nothing
     end
     # Insert leading zeros
-    bytes = node_bytes(ctx, node)
+    bytes = read_bytes(ctx, node)
     while length(bytes) < target_span
         insert!(bytes, 3, '0')
     end
@@ -92,7 +92,7 @@ function format_float_literals(ctx::Context, node::JuliaSyntax.GreenNode)
     JuliaSyntax.kind(node) in KSet"Float Float32" || return nothing
     @assert JuliaSyntax.flags(node) == 0
     @assert !JuliaSyntax.haschildren(node)
-    str = String(node_bytes(ctx, node))
+    str = String(read_bytes(ctx, node))
     # Check and shortcut the happy path first
     r = r"""
     ^