Index: flang/include/flang/Runtime/command.h
===================================================================
--- flang/include/flang/Runtime/command.h
+++ flang/include/flang/Runtime/command.h
@@ -48,8 +48,8 @@
 
 // Try to get the significant length of the environment variable specified by
 // NAME. Returns 0 if it doesn't manage.
-std::int64_t RTNAME(EnvVariableLength)(
-    const Descriptor &name, bool trim_name = true);
+std::int64_t RTNAME(EnvVariableLength)(const Descriptor &name,
+    bool trim_name = true, const char *sourceFile = nullptr, int line = 0);
 }
 } // namespace Fortran::runtime
 
Index: flang/runtime/command.cpp
===================================================================
--- flang/runtime/command.cpp
+++ flang/runtime/command.cpp
@@ -9,6 +9,7 @@
 #include "flang/Runtime/command.h"
 #include "environment.h"
 #include "stat.h"
+#include "terminator.h"
 #include "flang/Runtime/descriptor.h"
 #include <cstdlib>
 #include <limits>
@@ -89,15 +90,17 @@
   return s + 1;
 }
 
-std::int64_t RTNAME(EnvVariableLength)(const Descriptor &name, bool trim_name) {
+std::int64_t RTNAME(EnvVariableLength)(
+    const Descriptor &name, bool trim_name, const char *sourceFile, int line) {
   std::size_t nameLength{
       trim_name ? LengthWithoutTrailingSpaces(name) : name.ElementBytes()};
   if (nameLength == 0) {
     return 0;
   }
 
-  const char *value{
-      executionEnvironment.GetEnv(name.OffsetElement(), nameLength)};
+  Terminator terminator{sourceFile, line};
+  const char *value{executionEnvironment.GetEnv(
+      name.OffsetElement(), nameLength, terminator)};
   if (!value) {
     return 0;
   }
Index: flang/runtime/environment.h
===================================================================
--- flang/runtime/environment.h
+++ flang/runtime/environment.h
@@ -14,6 +14,8 @@
 
 namespace Fortran::runtime {
 
+class Terminator;
+
 #if FLANG_BIG_ENDIAN
 constexpr bool isHostLittleEndian{false};
 #elif FLANG_LITTLE_ENDIAN
@@ -29,7 +31,8 @@
 
 struct ExecutionEnvironment {
   void Configure(int argc, const char *argv[], const char *envp[]);
-  const char *GetEnv(const char *name, std::size_t name_length);
+  const char *GetEnv(
+      const char *name, std::size_t name_length, const Terminator &terminator);
 
   int argc;
   const char **argv;
@@ -37,6 +40,9 @@
   int listDirectedOutputLineLengthLimit;
   enum decimal::FortranRounding defaultOutputRoundingMode;
   Convert conversion;
+
+private:
+  const char *GetEnvFromEnvp(const char *name, std::size_t name_length);
 };
 extern ExecutionEnvironment executionEnvironment;
 } // namespace Fortran::runtime
Index: flang/runtime/environment.cpp
===================================================================
--- flang/runtime/environment.cpp
+++ flang/runtime/environment.cpp
@@ -7,7 +7,9 @@
 //===----------------------------------------------------------------------===//
 
 #include "environment.h"
+#include "memory.h"
 #include "tools.h"
+#include <cassert>
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
@@ -69,10 +71,9 @@
   // TODO: Set RP/ROUND='PROCESSOR_DEFINED' from environment
 }
 
-const char *ExecutionEnvironment::GetEnv(
+const char *ExecutionEnvironment::GetEnvFromEnvp(
     const char *name, std::size_t name_length) {
   if (!envp) {
-    // TODO: Ask std::getenv.
     return nullptr;
   }
 
@@ -90,6 +91,26 @@
       return eq + 1;
     }
   }
+
   return nullptr;
 }
+
+const char *ExecutionEnvironment::GetEnv(
+    const char *name, std::size_t name_length, const Terminator &terminator) {
+  assert(name_length && "Invalid environment variable name");
+
+  const char *value{GetEnvFromEnvp(name, name_length)};
+  if (value) {
+    return value;
+  }
+
+  // Try to read the environment directly. This is especially useful when
+  // ProgramStart was not invoked at all, e.g. when the main program is not
+  // Fortran.
+  OwningPtr<char> cStyleName{
+      SaveDefaultCharacter(name, name_length, terminator)};
+  assert(cStyleName && "Expected non-null pointer");
+
+  return std::getenv(cStyleName.get());
+}
 } // namespace Fortran::runtime
Index: flang/runtime/tools.cpp
===================================================================
--- flang/runtime/tools.cpp
+++ flang/runtime/tools.cpp
@@ -10,6 +10,7 @@
 #include "terminator.h"
 #include <algorithm>
 #include <cstdint>
+#include <cstdlib>
 #include <cstring>
 
 namespace Fortran::runtime {
Index: flang/unittests/Runtime/CommandTest.cpp
===================================================================
--- flang/unittests/Runtime/CommandTest.cpp
+++ flang/unittests/Runtime/CommandTest.cpp
@@ -11,6 +11,7 @@
 #include "gtest/gtest.h"
 #include "flang/Runtime/descriptor.h"
 #include "flang/Runtime/main.h"
+#include <cstdlib>
 
 using namespace Fortran::runtime;
 
@@ -204,4 +205,18 @@
       RTNAME(EnvVariableLength)(*CharDescriptor("NAME "), /*trim_name=*/false));
 
   EXPECT_EQ(0, RTNAME(EnvVariableLength)(*CharDescriptor("     ")));
+  EXPECT_EQ(0, RTNAME(EnvVariableLength)(*CharDescriptor("")));
+
+  // Test a variable that's expected to exist in the environment but isn't
+  // passed into ProgramStart's envp argument.
+  char *path{std::getenv("PATH")};
+  auto expectedLen{static_cast<int64_t>(std::strlen(path))};
+  EXPECT_EQ(expectedLen, RTNAME(EnvVariableLength)(*CharDescriptor("PATH")));
+}
+
+TEST(EnvironmentVariablesNoProgStart, Length) {
+  // Test a variable that's expected to exist in the environment.
+  char *path{std::getenv("PATH")};
+  auto expectedLen{static_cast<int64_t>(std::strlen(path))};
+  EXPECT_EQ(expectedLen, RTNAME(EnvVariableLength)(*CharDescriptor("PATH")));
 }