diff --git a/.github/workflows/nim-matrix.yml b/.github/workflows/nim-matrix.yml
index 0b57c8bf..579ee6a5 100644
--- a/.github/workflows/nim-matrix.yml
+++ b/.github/workflows/nim-matrix.yml
@@ -6,7 +6,7 @@ on:
 
 env:
   cache_nonce: 0 # Allows for easily busting actions/cache caches
-  nim_version: pinned, v1.6.16, v1.6.18
+  nim_version: pinned
 
 jobs:
   matrix:
diff --git a/Makefile b/Makefile
index 2e1f97ad..54ac04d2 100644
--- a/Makefile
+++ b/Makefile
@@ -15,7 +15,7 @@
 #
 # If NIM_COMMIT is set to "nimbusbuild", this will use the
 # version pinned by nimbus-build-system.
-PINNED_NIM_VERSION := v1.6.14
+PINNED_NIM_VERSION := 38640664088251bbc88917b4bacfd86ec53014b8 # 1.6.21
 
 ifeq ($(NIM_COMMIT),)
 NIM_COMMIT := $(PINNED_NIM_VERSION)
diff --git a/codex/erasure/asyncbackend.nim b/codex/erasure/asyncbackend.nim
index f3bca851..4827806a 100644
--- a/codex/erasure/asyncbackend.nim
+++ b/codex/erasure/asyncbackend.nim
@@ -114,7 +114,14 @@ proc proxySpawnEncodeTask(
   args: EncodeTaskArgs,
   data: ref seq[seq[byte]]
 ): Flowvar[EncodeTaskResult] =
-  tp.spawn encodeTask(args, data[])
+  # FIXME Uncomment the code below after addressing an issue:
+  # https://github.com/codex-storage/nim-codex/issues/854
+
+  # tp.spawn encodeTask(args, data[])
+
+  let fv = EncodeTaskResult.newFlowVar
+  fv.readyWith(encodeTask(args, data[]))
+  return fv
 
 proc proxySpawnDecodeTask(
   tp: Taskpool,
@@ -122,7 +129,14 @@ proc proxySpawnDecodeTask(
   data: ref seq[seq[byte]],
   parity: ref seq[seq[byte]]
 ): Flowvar[DecodeTaskResult] =
-  tp.spawn decodeTask(args, data[], parity[])
+  # FIXME Uncomment the code below after addressing an issue:
+  # https://github.com/codex-storage/nim-codex/issues/854
+  
+  # tp.spawn decodeTask(args, data[], parity[])
+
+  let fv = DecodeTaskResult.newFlowVar
+  fv.readyWith(decodeTask(args, data[], parity[]))
+  return fv
 
 proc awaitResult[T](signal: ThreadSignalPtr, handle: Flowvar[T]): Future[?!T] {.async.} =
   await wait(signal)
diff --git a/codex/erasure/erasure.nim b/codex/erasure/erasure.nim
index 0c921776..56e3e1cf 100644
--- a/codex/erasure/erasure.nim
+++ b/codex/erasure/erasure.nim
@@ -27,6 +27,7 @@ import ../blocktype as bt
 import ../utils
 import ../utils/asynciter
 import ../indexingstrategy
+import ../errors
 
 import pkg/stew/byteutils
 
@@ -82,6 +83,13 @@ type
     blocksCount: Natural
     strategy: StrategyType
 
+  ErasureError* = object of CodexError
+  InsufficientBlocksError* = object of ErasureError
+    # Minimum size, in bytes, that the dataset must have had
+    # for the encoding request to have succeeded with the parameters
+    # provided.
+    minSize*: NBytes
+
 func indexToPos(steps, idx, step: int): int {.inline.} =
   ## Convert an index to a position in the encoded
   ##  dataset
@@ -236,11 +244,13 @@ proc init*(
   ecK: Natural, ecM: Natural,
   strategy: StrategyType): ?!EncodingParams =
   if ecK > manifest.blocksCount:
-    return failure(
-      "Unable to encode manifest, not enough blocks, ecK = " &
+    let exc = (ref InsufficientBlocksError)(
+      msg: "Unable to encode manifest, not enough blocks, ecK = " &
       $ecK &
       ", blocksCount = " &
-      $manifest.blocksCount)
+      $manifest.blocksCount,
+      minSize: ecK.NBytes * manifest.blockSize)
+    return failure(exc)
 
   let
     rounded = roundUp(manifest.blocksCount, ecK)
diff --git a/codex/node.nim b/codex/node.nim
index 419228eb..4eb4cd0e 100644
--- a/codex/node.nim
+++ b/codex/node.nim
@@ -423,6 +423,15 @@ proc setupRequest(
     trace "Unable to fetch manifest for cid"
     return failure error
 
+  # ----------------------------------------------------------------------------
+  # FIXME this is a BAND-AID to address
+  #   https://github.com/codex-storage/nim-codex/issues/852 temporarily for the
+  #   workshop. Remove this once we get that fixed.
+  if manifest.blocksCount.uint == ecK:
+    return failure("Cannot setup slots for a dataset with ecK == numBlocks. Please use a larger file or a different combination of `nodes` and `tolerance`.")
+  # ----------------------------------------------------------------------------
+
+
   # Erasure code the dataset according to provided parameters
   let
     erasure = Erasure.new(
diff --git a/codex/rest/api.nim b/codex/rest/api.nim
index 6b258b22..d44cffa4 100644
--- a/codex/rest/api.nim
+++ b/codex/rest/api.nim
@@ -32,6 +32,7 @@ import ../node
 import ../blocktype
 import ../conf
 import ../contracts
+import ../erasure/erasure
 import ../manifest
 import ../streams/asyncstreamwrapper
 import ../stores
@@ -432,8 +433,16 @@ proc initPurchasingApi(node: CodexNodeRef, router: var RestRouter) =
         let nodes = params.nodes |? 1
         let tolerance = params.tolerance |? 0
 
-        if (nodes - tolerance) < 1:
-          return RestApiResponse.error(Http400, "Tolerance cannot be greater or equal than nodes (nodes - tolerance)")
+        # prevent underflow
+        if tolerance > nodes:
+          return RestApiResponse.error(Http400, "Invalid parameters: `tolerance` cannot be greater than `nodes`")
+
+        let ecK = nodes - tolerance
+        let ecM = tolerance # for readability
+
+        # ensure leopard constrainst of 1 < K ≥ M
+        if ecK <= 1 or ecK < ecM:
+          return RestApiResponse.error(Http400, "Invalid parameters: parameters must satify `1 < (nodes - tolerance) ≥ tolerance`")
 
         without expiry =? params.expiry:
           return RestApiResponse.error(Http400, "Expiry required")
@@ -451,6 +460,11 @@ proc initPurchasingApi(node: CodexNodeRef, router: var RestRouter) =
           params.collateral,
           expiry), error:
 
+          if error of InsufficientBlocksError:
+            return RestApiResponse.error(Http400,
+            "Dataset too small for erasure parameters, need at least " &
+              $(ref InsufficientBlocksError)(error).minSize.int & " bytes")
+
           return RestApiResponse.error(Http500, error.msg)
 
         return RestApiResponse.response(purchaseId.toHex)
diff --git a/tests/codex/testerasure.nim b/tests/codex/testerasure.nim
index 84f4b1c3..3febcfa5 100644
--- a/tests/codex/testerasure.nim
+++ b/tests/codex/testerasure.nim
@@ -252,3 +252,22 @@ suite "Erasure encode/decode":
       decoded.treeCid == manifest.treeCid
       decoded.treeCid == verifiable.originalTreeCid
       decoded.blocksCount == verifiable.originalBlocksCount
+
+  for i in 1..5:
+    test "Should encode/decode using various parameters " & $i & "/5":
+      let
+        blockSize   = rng.sample(@[1, 2, 4, 8, 16, 32, 64].mapIt(it.KiBs))
+        datasetSize = 1.MiBs
+        ecK         = 10.Natural
+        ecM         = 10.Natural
+
+      let
+        chunker = RandomChunker.new(rng, size = datasetSize, chunkSize = blockSize)
+        manifest = await storeDataGetManifest(store, chunker)
+        encoded = (await erasure.encode(manifest, ecK, ecM)).tryGet()
+        decoded = (await erasure.decode(encoded)).tryGet()
+
+      check:
+        decoded.treeCid == manifest.treeCid
+        decoded.treeCid == encoded.originalTreeCid
+        decoded.blocksCount == encoded.originalBlocksCount
diff --git a/tests/integration/codexclient.nim b/tests/integration/codexclient.nim
index bce1c27e..d2d78b46 100644
--- a/tests/integration/codexclient.nim
+++ b/tests/integration/codexclient.nim
@@ -96,7 +96,7 @@ proc requestStorageRaw*(
     proofProbability: UInt256,
     collateral: UInt256,
     expiry: uint = 0,
-    nodes: uint = 1,
+    nodes: uint = 2,
     tolerance: uint = 0
 ): Response =
 
@@ -125,7 +125,7 @@ proc requestStorage*(
     proofProbability: UInt256,
     expiry: uint,
     collateral: UInt256,
-    nodes: uint = 1,
+    nodes: uint = 2,
     tolerance: uint = 0
 ): ?!PurchaseId =
   ## Call request storage REST endpoint
diff --git a/tests/integration/testpurchasing.nim b/tests/integration/testpurchasing.nim
index 8f5a5bef..bc87f51b 100644
--- a/tests/integration/testpurchasing.nim
+++ b/tests/integration/testpurchasing.nim
@@ -8,7 +8,8 @@ import ../examples
 twonodessuite "Purchasing", debug1 = false, debug2 = false:
 
   test "node handles storage request":
-    let cid = client1.upload("some file contents").get
+    let data = await RandomChunker.example(blocks=2)
+    let cid = client1.upload(data).get
     let id1 = client1.requestStorage(cid, duration=100.u256, reward=2.u256, proofProbability=3.u256, expiry=10, collateral=200.u256).get
     let id2 = client1.requestStorage(cid, duration=400.u256, reward=5.u256, proofProbability=6.u256, expiry=10, collateral=201.u256).get
     check id1 != id2
@@ -26,7 +27,7 @@ twonodessuite "Purchasing", debug1 = false, debug2 = false:
       proofProbability=3.u256,
       expiry=30,
       collateral=200.u256,
-      nodes=2,
+      nodes=3,
       tolerance=1).get
 
     let request = client1.getPurchase(id).get.request.get
@@ -35,7 +36,7 @@ twonodessuite "Purchasing", debug1 = false, debug2 = false:
     check request.ask.proofProbability == 3.u256
     check request.expiry == 30
     check request.ask.collateral == 200.u256
-    check request.ask.slots == 2'u64
+    check request.ask.slots == 3'u64
     check request.ask.maxSlotLoss == 1'u64
 
   # TODO: We currently do not support encoding single chunks
@@ -52,7 +53,8 @@ twonodessuite "Purchasing", debug1 = false, debug2 = false:
   #   check request.ask.maxSlotLoss == 1'u64
 
   test "node remembers purchase status after restart":
-    let cid = client1.upload("some file contents").get
+    let data = await RandomChunker.example(blocks=2)
+    let cid = client1.upload(data).get
     let id = client1.requestStorage(cid,
                                     duration=100.u256,
                                     reward=2.u256,
@@ -71,25 +73,12 @@ twonodessuite "Purchasing", debug1 = false, debug2 = false:
     check request.ask.proofProbability == 3.u256
     check request.expiry == 30
     check request.ask.collateral == 200.u256
-    check request.ask.slots == 1'u64
+    check request.ask.slots == 2'u64
     check request.ask.maxSlotLoss == 0'u64
 
-  test "request storage fails if nodes and tolerance aren't correct":
-    let cid = client1.upload("some file contents").get
-    let responseBefore = client1.requestStorageRaw(cid,
-      duration=100.u256,
-      reward=2.u256,
-      proofProbability=3.u256,
-      expiry=30,
-      collateral=200.u256,
-      nodes=1,
-      tolerance=1)
-
-    check responseBefore.status == "400 Bad Request"
-    check responseBefore.body == "Tolerance cannot be greater or equal than nodes (nodes - tolerance)"
-
   test "node requires expiry and its value to be in future":
-    let cid = client1.upload("some file contents").get
+    let data = await RandomChunker.example(blocks=2)
+    let cid = client1.upload(data).get
 
     let responseMissing = client1.requestStorageRaw(cid, duration=1.u256, reward=2.u256, proofProbability=3.u256, collateral=200.u256)
     check responseMissing.status == "400 Bad Request"
diff --git a/tests/integration/testrestapi.nim b/tests/integration/testrestapi.nim
index 8c2c20e4..1834dcf2 100644
--- a/tests/integration/testrestapi.nim
+++ b/tests/integration/testrestapi.nim
@@ -1,7 +1,9 @@
+import std/httpclient
 import std/sequtils
 from pkg/libp2p import `==`
 import pkg/codex/units
 import ./twonodes
+import ../examples
 
 twonodessuite "REST API", debug1 = false, debug2 = false:
 
@@ -36,3 +38,93 @@ twonodessuite "REST API", debug1 = false, debug2 = false:
 
     check:
       [cid1, cid2].allIt(it in list.content.mapIt(it.cid))
+
+  test "request storage fails for datasets that are too small":
+    let cid = client1.upload("some file contents").get
+    let response = client1.requestStorageRaw(cid, duration=10.u256, reward=2.u256, proofProbability=3.u256, nodes=2, collateral=200.u256, expiry=9)
+
+    check:
+      response.status == "400 Bad Request"
+      response.body == "Dataset too small for erasure parameters, need at least "  & $(2*DefaultBlockSize.int) & " bytes"
+
+  test "request storage succeeds for sufficiently sized datasets":
+    let data = await RandomChunker.example(blocks=2)
+    let cid = client1.upload(data).get
+    let response = client1.requestStorageRaw(cid, duration=10.u256, reward=2.u256, proofProbability=3.u256, collateral=200.u256, expiry=9)
+
+    check:
+      response.status == "200 OK"
+
+  test "request storage fails if nodes and tolerance aren't correct":
+    let data = await RandomChunker.example(blocks=2)
+    let cid = client1.upload(data).get
+    let duration = 100.u256
+    let reward = 2.u256
+    let proofProbability = 3.u256
+    let expiry = 30.uint
+    let collateral = 200.u256
+    let ecParams = @[(1, 0), (1, 1), (2, 1), (3, 2), (3, 3)]
+
+    for ecParam in ecParams:
+      let (nodes, tolerance) = ecParam
+
+      var responseBefore = client1.requestStorageRaw(cid,
+        duration,
+        reward,
+        proofProbability,
+        collateral,
+        expiry,
+        nodes.uint,
+        tolerance.uint)
+
+      check responseBefore.status == "400 Bad Request"
+      check responseBefore.body == "Invalid parameters: parameters must satify `1 < (nodes - tolerance) ≥ tolerance`"
+
+  test "request storage fails if tolerance > nodes (underflow protection)":
+    let data = await RandomChunker.example(blocks=2)
+    let cid = client1.upload(data).get
+    let duration = 100.u256
+    let reward = 2.u256
+    let proofProbability = 3.u256
+    let expiry = 30.uint
+    let collateral = 200.u256
+    let ecParams = @[(0, 1), (1, 2), (2, 3)]
+
+    for ecParam in ecParams:
+      let (nodes, tolerance) = ecParam
+
+      var responseBefore = client1.requestStorageRaw(cid,
+        duration,
+        reward,
+        proofProbability,
+        collateral,
+        expiry,
+        nodes.uint,
+        tolerance.uint)
+
+      check responseBefore.status == "400 Bad Request"
+      check responseBefore.body == "Invalid parameters: `tolerance` cannot be greater than `nodes`"
+
+  test "request storage succeeds if nodes and tolerance within range":
+    let data = await RandomChunker.example(blocks=2)
+    let cid = client1.upload(data).get
+    let duration = 100.u256
+    let reward = 2.u256
+    let proofProbability = 3.u256
+    let expiry = 30.uint
+    let collateral = 200.u256
+    let ecParams = @[(2, 0), (3, 1), (5, 2)]
+
+    for ecParam in ecParams:
+      let (nodes, tolerance) = ecParam
+
+      var responseBefore = client1.requestStorageRaw(cid,
+        duration,
+        reward,
+        proofProbability,
+        collateral,
+        expiry,
+        nodes.uint,
+        tolerance.uint)
+
+      check responseBefore.status == "200 OK"