Index: flang/include/flang/Runtime/magic-numbers.h
===================================================================
--- flang/include/flang/Runtime/magic-numbers.h
+++ flang/include/flang/Runtime/magic-numbers.h
@@ -39,4 +39,12 @@
 #define FORTRAN_RUNTIME_STAT_STOPPED_IMAGE 104
 #define FORTRAN_RUNTIME_STAT_UNLOCKED 105
 #define FORTRAN_RUNTIME_STAT_UNLOCKED_FAILED_IMAGE 106
+
+#if 0
+Status codes for GET_COMMAND_ARGUMENT. The status for 'value too short' needs
+to be -1, the others must be positive.
+#endif
+#define FORTRAN_RUNTIME_STAT_INVALID_ARG_NUMBER 107
+#define FORTRAN_RUNTIME_STAT_MISSING_ARG 108
+#define FORTRAN_RUNTIME_STAT_VALUE_TOO_SHORT -1
 #endif
Index: flang/runtime/command.cpp
===================================================================
--- flang/runtime/command.cpp
+++ flang/runtime/command.cpp
@@ -8,6 +8,7 @@
 
 #include "flang/Runtime/command.h"
 #include "environment.h"
+#include "stat.h"
 #include "flang/Runtime/descriptor.h"
 #include <limits>
 
@@ -60,21 +61,21 @@
     if (IsValidCharDescriptor(value)) {
       FillWithSpaces(value);
     }
-    return 1;
+    return ToErrmsg(errmsg, StatInvalidArgumentNumber);
   }
 
   if (IsValidCharDescriptor(value)) {
     LengthType argLen{ArgumentLength(n)};
     if (argLen <= 0) {
       FillWithSpaces(value);
-      return 2;
+      return ToErrmsg(errmsg, StatMissingArgument);
     }
     if (argLen >= static_cast<LengthType>(value->ElementBytes())) {
-      return -1;
+      return ToErrmsg(errmsg, StatValueTooShort);
     }
     std::strncpy(
         value->OffsetElement(), executionEnvironment.argv[n], argLen + 1);
   }
-  return 0;
+  return StatOk;
 }
 } // namespace Fortran::runtime
Index: flang/runtime/stat.h
===================================================================
--- flang/runtime/stat.h
+++ flang/runtime/stat.h
@@ -44,6 +44,9 @@
   StatUnlockedFailedImage = FORTRAN_RUNTIME_STAT_UNLOCKED_FAILED_IMAGE,
 
   // Additional "processor-defined" STAT= values
+  StatInvalidArgumentNumber = FORTRAN_RUNTIME_STAT_INVALID_ARG_NUMBER,
+  StatMissingArgument = FORTRAN_RUNTIME_STAT_MISSING_ARG,
+  StatValueTooShort = FORTRAN_RUNTIME_STAT_VALUE_TOO_SHORT,
 };
 
 const char *StatErrorString(int);
Index: flang/runtime/stat.cpp
===================================================================
--- flang/runtime/stat.cpp
+++ flang/runtime/stat.cpp
@@ -50,6 +50,13 @@
   case StatUnlockedFailedImage:
     return "Failed image unlocked";
 
+  case StatInvalidArgumentNumber:
+    return "Invalid argument number";
+  case StatMissingArgument:
+    return "Missing argument";
+  case StatValueTooShort:
+    return "Value too short";
+
   default:
     return nullptr;
   }
Index: flang/unittests/Runtime/CommandTest.cpp
===================================================================
--- flang/unittests/Runtime/CommandTest.cpp
+++ flang/unittests/Runtime/CommandTest.cpp
@@ -7,13 +7,15 @@
 //===----------------------------------------------------------------------===//
 
 #include "flang/Runtime/command.h"
+#include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include "flang/Runtime/descriptor.h"
 #include "flang/Runtime/main.h"
 
 using namespace Fortran::runtime;
+using ::testing::StartsWith;
 
-template <std::size_t n = 128>
+template <std::size_t n = 64>
 static OwningPtr<Descriptor> CreateEmptyCharDescriptor() {
   OwningPtr<Descriptor> descriptor{Descriptor::Create(
       sizeof(char), n, nullptr, 0, nullptr, CFI_attribute_allocatable)};
@@ -37,14 +39,20 @@
     EXPECT_STREQ(value->OffsetElement(), argv);
   }
 
-  void CheckMissingArgumentValue(int n) const {
+  void CheckMissingArgumentValue(int n, const char *errStr = nullptr) const {
     OwningPtr<Descriptor> value{CreateEmptyCharDescriptor()};
     ASSERT_NE(value, nullptr);
 
-    EXPECT_GT(RTNAME(ArgumentValue)(n, value.get(), nullptr), 0);
+    OwningPtr<Descriptor> err{errStr ? CreateEmptyCharDescriptor() : nullptr};
+
+    EXPECT_GT(RTNAME(ArgumentValue)(n, value.get(), err.get()), 0);
 
     std::string spaces(value->ElementBytes(), ' ');
     EXPECT_STREQ(value->OffsetElement(), spaces.c_str());
+
+    if (errStr) {
+      EXPECT_THAT(err->OffsetElement(), StartsWith(errStr));
+    }
   }
 };
 
@@ -112,7 +120,6 @@
 TEST_F(SeveralArguments, ArgumentValue) {
   CheckArgumentValue(0, severalArgsArgv[0]);
   CheckArgumentValue(1, severalArgsArgv[1]);
-  CheckMissingArgumentValue(2);
   CheckArgumentValue(3, severalArgsArgv[3]);
   CheckArgumentValue(4, severalArgsArgv[4]);
 }
@@ -124,11 +131,26 @@
   EXPECT_GT(RTNAME(ArgumentValue)(-1, nullptr, nullptr), 0);
 }
 
-TEST_F(SeveralArguments, ArgumentValueErrors) {
-  CheckMissingArgumentValue(-1);
+TEST_F(SeveralArguments, MissingArguments) {
+  CheckMissingArgumentValue(-1, "Invalid argument number");
+  CheckMissingArgumentValue(2, "Missing argument");
+  CheckMissingArgumentValue(5, "Invalid argument number");
   CheckMissingArgumentValue(5);
+}
 
+TEST_F(SeveralArguments, ValueTooShort) {
   OwningPtr<Descriptor> tooShort{CreateEmptyCharDescriptor<16>()};
   ASSERT_NE(tooShort, nullptr);
   EXPECT_EQ(RTNAME(ArgumentValue)(1, tooShort.get(), nullptr), -1);
+
+  OwningPtr<Descriptor> errMsg{CreateEmptyCharDescriptor()};
+  ASSERT_NE(errMsg, nullptr);
+  EXPECT_EQ(RTNAME(ArgumentValue)(1, tooShort.get(), errMsg.get()), -1);
+  EXPECT_THAT(errMsg->OffsetElement(), StartsWith("Value too short"));
+}
+
+TEST_F(SeveralArguments, ErrMsgTooShort) {
+  OwningPtr<Descriptor> errMsg{CreateEmptyCharDescriptor<3>()};
+  EXPECT_GT(RTNAME(ArgumentValue)(-1, nullptr, errMsg.get()), 0);
+  EXPECT_STREQ(errMsg->OffsetElement(), "Inv");
 }