diff --git a/fuzzers/tint_common_fuzzer.cc b/fuzzers/tint_common_fuzzer.cc
index 88f0107dcf..590ff15dec 100644
--- a/fuzzers/tint_common_fuzzer.cc
+++ b/fuzzers/tint_common_fuzzer.cc
@@ -205,8 +205,8 @@ int CommonFuzzer::Run(const uint8_t* data, size_t size) {
       // sizeof(uint32_t)` uint32_t values. If `size` is not a multiple of
       // sizeof(uint32_t) then not all of `data` can be copied into
       // `spirv_input`, and any trailing bytes are discarded.
-      const size_t adjusted_size = (size / sizeof(uint32_t)) * sizeof(uint32_t);
-      std::memcpy(spirv_input.data(), data, adjusted_size);
+      std::memcpy(spirv_input.data(), data,
+                  spirv_input.size() * sizeof(uint32_t));
       if (spirv_input.empty()) {
         return 0;
       }
diff --git a/fuzzers/tint_spirv_tools_fuzzer/fuzzer.cc b/fuzzers/tint_spirv_tools_fuzzer/fuzzer.cc
index dac05dc918..6ca8b46fde 100644
--- a/fuzzers/tint_spirv_tools_fuzzer/fuzzer.cc
+++ b/fuzzers/tint_spirv_tools_fuzzer/fuzzer.cc
@@ -102,7 +102,8 @@ extern "C" size_t LLVMFuzzerCustomMutator(uint8_t* data,
                                           unsigned seed) {
   assert((size % 4) == 0 &&
          "A valid SPIR-V binary's size must be a multiple of 4, and the "
-         "SPIR-V Tools fuzzer should only work with valid binaries.");
+         "SPIR-V Tools fuzzer should only work with valid binaries. Check that "
+         "the fuzzer has been correctly configured.");
 
   std::vector<uint32_t> binary(size / sizeof(uint32_t));
   std::memcpy(binary.data(), data, size);
@@ -175,8 +176,10 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
   }
 
   assert((size % 4) == 0 &&
-         "A valid SPIR-V binary's size is a multiple of 4 bytes, and the "
-         "SPIR-V Tools fuzzer should only work with valid binaries.");
+         "By design, the SPIR-V Tools fuzzer should only ever test using valid "
+         "SPIR-V binaries, whose sizes should be multiples of 4 bytes. Check "
+         "that the fuzzer has been configured correctly, with a corpus of "
+         "valid SPIR-V binaries, and with only the custom mutator enabled.");
 
   CommonFuzzer spv_to_wgsl(InputFormat::kSpv, OutputFormat::kWGSL);
   spv_to_wgsl.EnableInspector();