diff --git a/manifest-schema.graphql b/manifest-schema.graphql
index b01ead799..837994f71 100644
--- a/manifest-schema.graphql
+++ b/manifest-schema.graphql
@@ -42,6 +42,7 @@ type EthereumContractAbi {
 
 type EthereumBlockHandler {
   handler: String!
+  blockFormat: String
   filter: EthereumBlockFilter
 }
 
diff --git a/src/subgraph.js b/src/subgraph.js
index 53e402ab6..32ab3cbef 100644
--- a/src/subgraph.js
+++ b/src/subgraph.js
@@ -6,6 +6,7 @@ let { strOptions } = require('yaml/types')
 let graphql = require('graphql/language')
 let validation = require('./validation')
 let ABI = require('./abi')
+let asc = require('assemblyscript')
 
 const throwCombinedError = (filename, errors) => {
   throw new Error(
@@ -23,6 +24,13 @@ const throwCombinedError = (filename, errors) => {
   )
 }
 
+// Define conversions from a 'blockFormat' value in the manifest to its corresponding struct name
+const blockFormatToStructName = immutable.Map({
+  'block-only': 'Block',
+  'block-with-transactions': 'BlockWithTransactions',
+  'block-with-receipts': 'BlockWithReceipts',
+})
+
 const buildCombinedWarning = (filename, warnings) =>
   warnings.size > 0
     ? warnings.reduce(
@@ -317,6 +325,91 @@ ${abiFunctions
       }, immutable.List())
   }
 
+  static validateBlockFunctions(manifest, { resolveFile }) {
+    return manifest
+      .get('dataSources')
+      .filter(
+        dataSource =>
+          dataSource.get('kind') === 'ethereum/contract' &&
+          dataSource.getIn(['mapping', 'blockHandlers'], immutable.List()).count() > 0,
+      )
+      .reduce((errors, dataSource, dataSourceIndex) => {
+        let path = ['dataSources', dataSourceIndex, 'blockHandlers']
+        // Use the Assemblyscript parser to generate an AST from the mapping file
+        let mappingFile = dataSource.getIn(['mapping', 'file'])
+        let mappingParser = new asc.Parser()
+        mappingParser.parseFile(
+          fs.readFileSync(resolveFile(mappingFile), 'utf-8'),
+          '',
+          false,
+        )
+
+        let blockHandlers = dataSource.getIn(
+          ['mapping', 'blockHandlers'],
+          immutable.List(),
+        )
+
+        // Ensure each blockHandler has a corresponding mapping handler
+        // with a compatible function signature and uses a supported `blockFormat` value.
+        return errors.concat(
+          blockHandlers.reduce(
+            (errors, handler, index) =>
+              mappingParser.program.sources
+                .filter(source => source.kind == asc.SourceKind.DEFAULT)
+                .some(source =>
+                  source.statements
+                    .filter(
+                      statement => statement.kind === asc.NodeKind.FUNCTIONDECLARATION,
+                    )
+                    .some(
+                      functionDeclaration =>
+                        functionDeclaration.name.text === handler.get('handler') &&
+                        functionDeclaration.signature.parameters.length === 1 &&
+                        functionDeclaration.signature.parameters[0].type.name.identifier
+                          .text === 'ethereum' &&
+                        functionDeclaration.signature.parameters[0].type.name.next
+                          .identifier.text ===
+                          blockFormatToStructName.get(
+                            handler.get('blockFormat', 'block-only'),
+                          ) &&
+                        functionDeclaration.signature.parameters[0].type.name.next
+                          .next === null &&
+                        functionDeclaration.signature.returnType.name.identifier.text ===
+                          'void',
+                    ),
+                )
+                ? errors
+                : blockFormatToStructName.get(handler.get('blockFormat', 'block-only'))
+                ? errors.push(
+                    immutable.fromJS({
+                      path: [...path, index],
+                      message: `\
+Matching mapping handler not found in '${mappingFile}' for blockHandler: '${handler.get(
+                        'handler',
+                      )}'.
+Signature:
+  ${handler.get('handler')}(block: ethereum.${blockFormatToStructName.get(
+                        handler.get('blockFormat', 'block-only'),
+                      )}): void`,
+                    }),
+                  )
+                : errors.push(
+                    immutable.fromJS({
+                      path: [...path, index],
+                      message: `Unsupported blockFormat, '${handler.get(
+                        'blockFormat',
+                      )}', specified for the '${handler.get('handler')}' blockHandler. 
+Please use one of the supported blockFormats: ${JSON.stringify(
+                        blockFormatToStructName.keySeq(),
+                      )}`,
+                    }),
+                  ),
+            immutable.List(),
+          ),
+        )
+      }, immutable.List())
+  }
+
   static validateRepository(manifest, { resolveFile }) {
     return manifest.get('repository') !==
       'https://github.com/graphprotocol/example-subgraph'
@@ -446,6 +539,7 @@ More than one template named '${name}', template names must be unique.`,
           ...Subgraph.validateEthereumContractHandlers(manifest),
           ...Subgraph.validateEvents(manifest, { resolveFile }),
           ...Subgraph.validateCallFunctions(manifest, { resolveFile }),
+          ...Subgraph.validateBlockFunctions(manifest, { resolveFile }),
           ...Subgraph.validateUniqueDataSourceNames(manifest),
           ...Subgraph.validateUniqueTemplateNames(manifest),
         )
diff --git a/tests/cli/validation.test.js b/tests/cli/validation.test.js
index f1947cd92..02c5d9e95 100644
--- a/tests/cli/validation.test.js
+++ b/tests/cli/validation.test.js
@@ -197,4 +197,13 @@ describe('Validation', () => {
       exitCode: 1,
     },
   )
+
+  cliTest(
+    'Block handler with incompatible mapping function',
+    ['codegen', '--skip-migrations'],
+    'validation/block-handler-with-incompatible-mapping-function',
+    {
+      exitCode: 1,
+    },
+  )
 })
diff --git a/tests/cli/validation/block-handler-with-incompatible-mapping-function.stderr b/tests/cli/validation/block-handler-with-incompatible-mapping-function.stderr
new file mode 100644
index 000000000..34cafba50
--- /dev/null
+++ b/tests/cli/validation/block-handler-with-incompatible-mapping-function.stderr
@@ -0,0 +1,7 @@
+- Load subgraph from subgraph.yaml
+✖ Failed to load subgraph from subgraph.yaml: Error in subgraph.yaml:
+
+  Path: dataSources > 0 > blockHandlers > 0
+  Matching mapping handler not found in './mapping.ts' for blockHandler: 'handleBlock'.
+  Signature:
+    handleBlock(block: ethereum.BlockWithTransactions): void
diff --git a/tests/cli/validation/block-handler-with-incompatible-mapping-function/Abi.json b/tests/cli/validation/block-handler-with-incompatible-mapping-function/Abi.json
new file mode 100644
index 000000000..4d05f5839
--- /dev/null
+++ b/tests/cli/validation/block-handler-with-incompatible-mapping-function/Abi.json
@@ -0,0 +1,7 @@
+[
+  {
+    "type": "event",
+    "name": "ExampleEvent",
+    "inputs": [{ "type": "string" }]
+  }
+]
diff --git a/tests/cli/validation/block-handler-with-incompatible-mapping-function/mapping.ts b/tests/cli/validation/block-handler-with-incompatible-mapping-function/mapping.ts
new file mode 100644
index 000000000..55376e559
--- /dev/null
+++ b/tests/cli/validation/block-handler-with-incompatible-mapping-function/mapping.ts
@@ -0,0 +1,9 @@
+import { ethereum } from '@graphprotocol/graph-ts'
+import { ExampleBlockEntity } from './generated/schema'
+
+export function handleBlock(block: ethereum.BlockWithReceipts): void {
+  let entity = new ExampleBlockEntity(block.hash.toHexString())
+  entity.number = block.number
+  entity.hash = block.hash
+  entity.save()
+}
\ No newline at end of file
diff --git a/tests/cli/validation/block-handler-with-incompatible-mapping-function/schema.graphql b/tests/cli/validation/block-handler-with-incompatible-mapping-function/schema.graphql
new file mode 100644
index 000000000..96ba50b79
--- /dev/null
+++ b/tests/cli/validation/block-handler-with-incompatible-mapping-function/schema.graphql
@@ -0,0 +1,5 @@
+type ExampleBlockEntity @entity {
+  id: ID!
+  number: BigInt!
+  hash: Bytes!
+}
diff --git a/tests/cli/validation/block-handler-with-incompatible-mapping-function/subgraph.yaml b/tests/cli/validation/block-handler-with-incompatible-mapping-function/subgraph.yaml
new file mode 100644
index 000000000..66d422fe0
--- /dev/null
+++ b/tests/cli/validation/block-handler-with-incompatible-mapping-function/subgraph.yaml
@@ -0,0 +1,22 @@
+specVersion: 0.0.1
+schema:
+  file: ./schema.graphql
+dataSources:
+- kind: ethereum/contract
+  name: ExampleSubgraph
+  network: mainnet
+  source:
+    abi: ExampleContract
+  mapping:
+    kind: ethereum/events
+    apiVersion: 0.0.1
+    language: wasm/assemblyscript
+    file: ./mapping.ts
+    entities:
+    - ExampleBlockEntity
+    abis:
+    - name: ExampleContract
+      file: ./Abi.json
+    blockHandlers:
+    - handler: handleBlock
+      blockFormat: block-with-transactions
\ No newline at end of file