diff --git a/libc/src/string/strstr.cpp b/libc/src/string/strstr.cpp
--- a/libc/src/string/strstr.cpp
+++ b/libc/src/string/strstr.cpp
@@ -16,6 +16,11 @@
 // TODO: This is a simple brute force implementation. This can be
 // improved upon using well known string matching algorithms.
 char *LLVM_LIBC_ENTRYPOINT(strstr)(const char *haystack, const char *needle) {
+  // The standard requires that haystack is returned if the needle is an empty
+  // string.
+  if (*needle == '\0')
+    return const_cast<char *>(haystack);
+
   for (size_t i = 0; haystack[i]; ++i) {
     size_t j;
     for (j = 0; haystack[i + j] && haystack[i + j] == needle[j]; ++j)
diff --git a/libc/utils/UnitTest/Test.cpp b/libc/utils/UnitTest/Test.cpp
--- a/libc/utils/UnitTest/Test.cpp
+++ b/libc/utils/UnitTest/Test.cpp
@@ -242,6 +242,10 @@
 bool Test::testStrEq(RunContext &Ctx, const char *LHS, const char *RHS,
                      const char *LHSStr, const char *RHSStr, const char *File,
                      unsigned long Line) {
+  if (LHS == nullptr)
+    LHS = "<nullptr>";
+  if (RHS == nullptr)
+    RHS = "<nullptr>";
   return internal::test(Ctx, Cond_EQ, llvm::StringRef(LHS),
                         llvm::StringRef(RHS), LHSStr, RHSStr, File, Line);
 }
@@ -249,6 +253,10 @@
 bool Test::testStrNe(RunContext &Ctx, const char *LHS, const char *RHS,
                      const char *LHSStr, const char *RHSStr, const char *File,
                      unsigned long Line) {
+  if (LHS == nullptr)
+    LHS = "<nullptr>";
+  if (RHS == nullptr)
+    RHS = "<nullptr>";
   return internal::test(Ctx, Cond_NE, llvm::StringRef(LHS),
                         llvm::StringRef(RHS), LHSStr, RHSStr, File, Line);
 }