diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 74a5553ce6e4..c874a84e0cbe 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -3055,7 +3055,9 @@ std::error_code BitcodeReader::rememberAndSkipFunctionBodies() {
   if (Stream.AtEndOfStream())
     return error("Could not find function in stream");
 
-  assert(SeenFirstFunctionBody);
+  if (!SeenFirstFunctionBody)
+    return error("Trying to materialize functions before seeing function blocks");
+
   // An old bitcode file with the symbol table at the end would have
   // finished the parse greedily.
   assert(SeenValueSymbolTable);
diff --git a/llvm/test/Bitcode/Inputs/invalid-no-function-block.bc b/llvm/test/Bitcode/Inputs/invalid-no-function-block.bc
new file mode 100644
index 000000000000..52b65588e4a7
Binary files /dev/null and b/llvm/test/Bitcode/Inputs/invalid-no-function-block.bc differ
diff --git a/llvm/test/Bitcode/invalid.test b/llvm/test/Bitcode/invalid.test
index 69104046df20..24ccd8bccd5b 100644
--- a/llvm/test/Bitcode/invalid.test
+++ b/llvm/test/Bitcode/invalid.test
@@ -207,3 +207,8 @@ RUN: not llvm-dis -disable-output %p/Inputs/invalid-alias-type-mismatch.bc 2>&1
 RUN:   FileCheck --check-prefix=ALIAS-TYPE-MISMATCH %s
 
 ALIAS-TYPE-MISMATCH: Alias and aliasee types don't match
+
+RUN: not llvm-dis -disable-output %p/Inputs/invalid-no-function-block.bc 2>&1 | \
+RUN:   FileCheck --check-prefix=NO-FUNCTION-BLOCK %s
+
+NO-FUNCTION-BLOCK: Trying to materialize functions before seeing function blocks