diff --git a/src/Prometheus.jl b/src/Prometheus.jl
index 916cdc3..4dc3346 100644
--- a/src/Prometheus.jl
+++ b/src/Prometheus.jl
@@ -202,7 +202,7 @@ function collect!(metrics::Vector, counter::Counter)
     push!(metrics,
         Metric(
             "counter", counter.metric_name, counter.help,
-            nothing, Sample(nothing, nothing, @atomic(counter.value)),
+            Sample(nothing, nothing, nothing, @atomic(counter.value)),
         ),
     )
     return metrics
@@ -310,7 +310,7 @@ function collect!(metrics::Vector, gauge::Gauge)
     push!(metrics,
         Metric(
             "gauge", gauge.metric_name, gauge.help,
-            nothing, Sample(nothing, nothing, @atomic(gauge.value)),
+            Sample(nothing, nothing, nothing, @atomic(gauge.value)),
         ),
     )
     return metrics
@@ -381,10 +381,10 @@ end
 function collect!(metrics::Vector, summary::Summary)
     push!(metrics,
         Metric(
-            "summary", summary.metric_name, summary.help, nothing,
+            "summary", summary.metric_name, summary.help,
             [
-                Sample("_count", nothing, @atomic(summary._count)),
-                Sample("_sum", nothing, @atomic(summary._sum)),
+                Sample("_count", nothing, nothing, @atomic(summary._count)),
+                Sample("_sum", nothing, nothing, @atomic(summary._sum)),
             ]
         ),
     )
@@ -748,8 +748,9 @@ function collect!(metrics::Vector, family::Family{C}) where C
     type = prometheus_type(C)
     samples = Sample[]
     buf = Metric[]
+    label_names = family.label_names
     @lock family.lock begin
-        for (labels, child) in family.children
+        for (label_values, child) in family.children
             # collect!(...) the child, throw away the metric, but keep the samples
             child_metrics = collect!(resize!(buf, 0), child)
             length(child_metrics) != 1 && unreachable() # TODO: maybe this should be supported?
@@ -758,12 +759,12 @@ function collect!(metrics::Vector, family::Family{C}) where C
             # Unwrap and rewrap samples with the labels
             child_samples = child_metric.samples
             if child_samples isa Sample
-                push!(samples, Sample(child_samples.suffix, labels, child_samples.value))
+                push!(samples, Sample(child_samples.suffix, label_names, label_values, child_samples.value))
             else
                 @assert(child_samples isa Vector{Sample})
                 for child_sample in child_samples
                     @assert(child_sample.label_values === nothing)
-                    push!(samples, Sample(child_sample.suffix, labels, child_sample.value))
+                    push!(samples, Sample(child_sample.suffix, label_names, label_values, child_sample.value))
                 end
             end
         end
@@ -776,7 +777,7 @@ function collect!(metrics::Vector, family::Family{C}) where C
     end)
     push!(
         metrics,
-        Metric(type, family.metric_name, family.help, family.label_names, samples),
+        Metric(type, family.metric_name, family.help, samples),
     )
     return metrics
 end
@@ -788,6 +789,7 @@ end
 
 struct Sample
     suffix::Union{String, Nothing} # e.g. _count or _sum
+    label_names::Union{LabelNames, Nothing}
     label_values::Union{LabelValues, Nothing}
     value::Float64
 end
@@ -796,7 +798,6 @@ struct Metric
     type::String
     metric_name::String
     help::String
-    label_names::Union{LabelNames, Nothing}
     # TODO: Union{Tuple{Sample}, Vector{Sample}} would always make this iterable.
     samples::Union{Sample, Vector{Sample}}
 end
@@ -817,11 +818,10 @@ function expose_metric(io::IO, metric::Metric)
     print_escaped(io, metric.help, ('\\', '\n'))
     println(io)
     println(io, "# TYPE ", metric.metric_name, " ", metric.type)
-    label_names = metric.label_names
     samples = metric.samples
     if samples isa Sample
         # Single sample, no labels
-        @assert(label_names === nothing)
+        @assert(samples.label_names === nothing)
         @assert(samples.label_values === nothing)
         @assert(samples.suffix === nothing)
         val = samples.value
@@ -837,11 +837,13 @@ function expose_metric(io::IO, metric::Metric)
                 print(io, sample.suffix)
             end
             # Print potential labels
-            labels = sample.label_values
-            if label_names !== nothing && labels !== nothing
+            label_names = sample.label_names
+            label_values = sample.label_values
+            @assert((label_names === nothing) === (label_values === nothing))
+            if label_names !== nothing && label_values !== nothing
                 first = true
                 print(io, "{")
-                for (name, value) in zip(label_names.label_names, labels.label_values)
+                for (name, value) in zip(label_names.label_names, label_values.label_values)
                     first || print(io, ",")
                     print(io, name, "=\"")
                     print_escaped(io, value, ('\\', '\"', '\n'))
diff --git a/src/gc_collector.jl b/src/gc_collector.jl
index bb95e74..e5a15ab 100644
--- a/src/gc_collector.jl
+++ b/src/gc_collector.jl
@@ -44,40 +44,42 @@ function collect!(metrics::Vector, ::GCCollector)
     gc_live_bytes = Base.gc_live_bytes()
     # Push all the metrics
     push!(metrics,
-        Metric(
-            "counter", "julia_gc_alloc_total", "Total number of allocations (calls to malloc, realloc, etc)",
-            LabelNames(("type",)),
-            [
-                Sample(nothing, LabelValues(("bigalloc",)), gc_num.bigalloc),
-                Sample(nothing, LabelValues(("malloc",)), gc_num.malloc),
-                Sample(nothing, LabelValues(("poolalloc",)), gc_num.poolalloc),
-                Sample(nothing, LabelValues(("realloc",)), gc_num.realloc),
-            ],
-        ),
+        let label_names = LabelNames(("type",))
+            Metric(
+                "counter", "julia_gc_alloc_total", "Total number of allocations (calls to malloc, realloc, etc)",
+                [
+                    Sample(nothing, label_names, LabelValues(("bigalloc",)), gc_num.bigalloc),
+                    Sample(nothing, label_names, LabelValues(("malloc",)), gc_num.malloc),
+                    Sample(nothing, label_names, LabelValues(("poolalloc",)), gc_num.poolalloc),
+                    Sample(nothing, label_names, LabelValues(("realloc",)), gc_num.realloc),
+                ],
+            )
+        end,
         Metric(
             "counter", "julia_gc_free_total", "Total number of calls to free()",
-            nothing, Sample(nothing, nothing, gc_num.freecall),
-        ),
-        Metric(
-            "counter", "julia_gc_alloc_bytes_total", "Total number of allocated bytes", nothing,
-            Sample(nothing, nothing, Base.gc_total_bytes(gc_num)),
+            Sample(nothing, nothing, nothing, gc_num.freecall),
         ),
         Metric(
-            "gauge", "julia_gc_live_bytes", "Current number of live bytes", nothing,
-            Sample(nothing, nothing, gc_live_bytes),
+            "counter", "julia_gc_alloc_bytes_total", "Total number of allocated bytes",
+            Sample(nothing, nothing, nothing, Base.gc_total_bytes(gc_num)),
         ),
         Metric(
-            "counter", "julia_gc_seconds_total", "Total time spent in garbage collection", nothing,
-            Sample(nothing, nothing, gc_num.total_time / 10^9), # [ns] to [s]
+            "gauge", "julia_gc_live_bytes", "Current number of live bytes",
+            Sample(nothing, nothing, nothing, gc_live_bytes),
         ),
         Metric(
-            "counter", "julia_gc_collections_total", "Total number of calls to garbage collection",
-            LabelNames(("type",)),
-            [
-                Sample(nothing, LabelValues(("full",)), gc_num.full_sweep),
-                Sample(nothing, LabelValues(("minor",)), gc_num.pause - gc_num.full_sweep),
-            ],
+            "counter", "julia_gc_seconds_total", "Total time spent in garbage collection",
+            Sample(nothing, nothing, nothing, gc_num.total_time / 10^9), # [ns] to [s]
         ),
+        let label_names = LabelNames(("type",))
+            Metric(
+                "counter", "julia_gc_collections_total", "Total number of calls to garbage collection",
+                [
+                    Sample(nothing, label_names, LabelValues(("full",)), gc_num.full_sweep),
+                    Sample(nothing, label_names, LabelValues(("minor",)), gc_num.pause - gc_num.full_sweep),
+                ],
+            )
+        end,
     )
     return metrics
 end
diff --git a/src/process_collector.jl b/src/process_collector.jl
index 2717651..8bb19b5 100644
--- a/src/process_collector.jl
+++ b/src/process_collector.jl
@@ -118,13 +118,13 @@ function collect!(metrics::Vector, procc::ProcessCollector)
         if procc.clock_ticks_per_second > 0
             utime = parse(Int, fields[14 - 2]) / procc.clock_ticks_per_second
             stime = parse(Int, fields[15 - 2]) / procc.clock_ticks_per_second
+            label_names = LabelNames(("mode",))
             proc_cpu_seconds = Metric(
                 "counter", "process_cpu_seconds_total",
                 "Total CPU time (user and system mode) in seconds.",
-                LabelNames(("mode",)),
                 [
-                    Sample(nothing, LabelValues(("system",)), stime),
-                    Sample(nothing, LabelValues(("user",)), utime),
+                    Sample(nothing, label_names, LabelValues(("system",)), stime),
+                    Sample(nothing, label_names, LabelValues(("user",)), utime),
                 ],
             )
             push!(metrics, proc_cpu_seconds)
@@ -132,16 +132,16 @@ function collect!(metrics::Vector, procc::ProcessCollector)
             starttime = parse(Int, fields[22 - 2]) / procc.clock_ticks_per_second
             proc_start_time = Metric(
                 "gauge", "process_start_time_seconds",
-                "Start time since unix epoch in seconds.", nothing,
-                Sample(nothing, nothing, starttime + procc.system_boot_time),
+                "Start time since unix epoch in seconds.",
+                Sample(nothing, nothing, nothing, starttime + procc.system_boot_time),
             )
             push!(metrics, proc_start_time)
         end
         # Virtual memory
         vsize = parse(Int, fields[23 - 2])
         proc_virtual_memory = Metric(
-            "gauge", "process_virtual_memory_bytes", "Virtual memory size in bytes.", nothing,
-            Sample(nothing, nothing, vsize),
+            "gauge", "process_virtual_memory_bytes", "Virtual memory size in bytes.",
+            Sample(nothing, nothing, nothing, vsize),
         )
         push!(metrics, proc_virtual_memory)
         if procc.pagesize > 0
@@ -149,8 +149,8 @@ function collect!(metrics::Vector, procc::ProcessCollector)
             rss = parse(Int, fields[24 - 2])
             proc_resident_memory = Metric(
                 "gauge", "process_resident_memory_bytes",
-                "Resident memory size (RSS) in bytes.", nothing,
-                Sample(nothing, nothing, rss * procc.pagesize),
+                "Resident memory size (RSS) in bytes.",
+                Sample(nothing, nothing, nothing, rss * procc.pagesize),
             )
             push!(metrics, proc_resident_memory)
         end
@@ -166,8 +166,8 @@ function collect!(metrics::Vector, procc::ProcessCollector)
         # Open file descriptors
         proc_open_fds = Metric(
             "gauge", "process_open_fds",
-            "Number of open file descriptors.", nothing,
-            Sample(nothing, nothing, proc_fd),
+            "Number of open file descriptors.",
+            Sample(nothing, nothing, nothing, proc_fd),
         )
         push!(metrics, proc_open_fds)
         # TODO: Maybe add maximum open fds from /proc/$(pid)/limits like the Python client
@@ -184,8 +184,8 @@ function collect!(metrics::Vector, procc::ProcessCollector)
         if rchar !== nothing
             proc_io_rchar = Metric(
                 "counter", "process_io_rchar_bytes_total",
-                "Total number of bytes read in bytes (rchar from /proc/[pid]/io).", nothing,
-                Sample(nothing, nothing, parse(Int, rchar.captures[1]::AbstractString)),
+                "Total number of bytes read in bytes (rchar from /proc/[pid]/io).",
+                Sample(nothing, nothing, nothing, parse(Int, rchar.captures[1]::AbstractString)),
             )
             push!(metrics, proc_io_rchar)
         end
@@ -193,8 +193,8 @@ function collect!(metrics::Vector, procc::ProcessCollector)
         if wchar !== nothing
             proc_io_wchar = Metric(
                 "counter", "process_io_wchar_bytes_total",
-                "Total number of bytes written in bytes (wchar from /proc/[pid]/io).", nothing,
-                Sample(nothing, nothing, parse(Int, wchar.captures[1]::AbstractString)),
+                "Total number of bytes written in bytes (wchar from /proc/[pid]/io).",
+                Sample(nothing, nothing, nothing, parse(Int, wchar.captures[1]::AbstractString)),
             )
             push!(metrics, proc_io_wchar)
         end
@@ -202,8 +202,8 @@ function collect!(metrics::Vector, procc::ProcessCollector)
         if syscr !== nothing
             proc_io_syscr = Metric(
                 "counter", "process_io_syscr_total",
-                "Total number of read I/O operations (syscalls) (syscr from /proc/[pid]/io).", nothing,
-                Sample(nothing, nothing, parse(Int, syscr.captures[1]::AbstractString)),
+                "Total number of read I/O operations (syscalls) (syscr from /proc/[pid]/io).",
+                Sample(nothing, nothing, nothing, parse(Int, syscr.captures[1]::AbstractString)),
             )
             push!(metrics, proc_io_syscr)
         end
@@ -211,8 +211,8 @@ function collect!(metrics::Vector, procc::ProcessCollector)
         if syscw !== nothing
             proc_io_syscw = Metric(
                 "counter", "process_io_syscw_total",
-                "Total number of write I/O operations (syscalls) (syscw from /proc/[pid]/io).", nothing,
-                Sample(nothing, nothing, parse(Int, syscw.captures[1]::AbstractString)),
+                "Total number of write I/O operations (syscalls) (syscw from /proc/[pid]/io).",
+                Sample(nothing, nothing, nothing, parse(Int, syscw.captures[1]::AbstractString)),
             )
             push!(metrics, proc_io_syscw)
         end
@@ -220,8 +220,8 @@ function collect!(metrics::Vector, procc::ProcessCollector)
         if read_bytes !== nothing
             proc_io_read_bytes = Metric(
                 "counter", "process_io_read_bytes_total",
-                "Total number of bytes read from the file system (read_bytes from /proc/[pid]/io).", nothing,
-                Sample(nothing, nothing, parse(Int, read_bytes.captures[1]::AbstractString)),
+                "Total number of bytes read from the file system (read_bytes from /proc/[pid]/io).",
+                Sample(nothing, nothing, nothing, parse(Int, read_bytes.captures[1]::AbstractString)),
             )
             push!(metrics, proc_io_read_bytes)
         end
@@ -229,8 +229,8 @@ function collect!(metrics::Vector, procc::ProcessCollector)
         if write_bytes !== nothing
             proc_io_write_bytes = Metric(
                 "counter", "process_io_write_bytes_total",
-                "Total number of bytes written to the file system (write_bytes from /proc/[pid]/io).", nothing,
-                Sample(nothing, nothing, parse(Int, write_bytes.captures[1]::AbstractString)),
+                "Total number of bytes written to the file system (write_bytes from /proc/[pid]/io).",
+                Sample(nothing, nothing, nothing, parse(Int, write_bytes.captures[1]::AbstractString)),
             )
             push!(metrics, proc_io_write_bytes)
         end