diff --git a/include/swift/AST/DiagnosticsFrontend.def b/include/swift/AST/DiagnosticsFrontend.def
index d2b19423778..421c4c54a73 100644
--- a/include/swift/AST/DiagnosticsFrontend.def
+++ b/include/swift/AST/DiagnosticsFrontend.def
@@ -209,6 +209,10 @@ ERROR(symbol_in_ir_not_in_tbd,none,
       "symbol '%0' (%1) is in generated IR file, but not in TBD file",
       (StringRef, StringRef))
 
+ERROR(redundant_prefix_compilation_flag,none,
+      "invalid argument '-D%0'; did you provide a redundant '-D' in your build settings?", 
+      (StringRef))    
+
 ERROR(invalid_conditional_compilation_flag,none,
       "conditional compilation flags must be valid Swift identifiers (rather than '%0')",
       (StringRef))
diff --git a/lib/Driver/Driver.cpp b/lib/Driver/Driver.cpp
index c4186b8100b..e5068b8824b 100644
--- a/lib/Driver/Driver.cpp
+++ b/lib/Driver/Driver.cpp
@@ -192,6 +192,9 @@ static void validateArgs(DiagnosticEngine &diags, const ArgList &Args) {
       diags.diagnose(SourceLoc(),
                      diag::cannot_assign_value_to_conditional_compilation_flag,
                      name);
+    else if (name.startswith("-D"))
+      diags.diagnose(SourceLoc(), diag::redundant_prefix_compilation_flag,
+                     name);
     else if (!Lexer::isIdentifier(name))
       diags.diagnose(SourceLoc(), diag::invalid_conditional_compilation_flag,
                      name);
diff --git a/test/Frontend/unknown-arguments.swift b/test/Frontend/unknown-arguments.swift
index e8f8553771e..c857177de76 100644
--- a/test/Frontend/unknown-arguments.swift
+++ b/test/Frontend/unknown-arguments.swift
@@ -10,5 +10,5 @@
 // RUN: not %swiftc_driver -D Correct -DAlsoCorrect -D@#%! -D Swift=Cool -D-D -c %s -o %t.o 2>&1 | %FileCheck -check-prefix=INVALID-COND %s
 // INVALID-COND: <unknown>:0: error: conditional compilation flags must be valid Swift identifiers (rather than '@#%!')
 // INVALID-COND-NEXT: <unknown>:0: warning: conditional compilation flags do not have values in Swift; they are either present or absent (rather than 'Swift=Cool')
-// INVALID-COND-NEXT: <unknown>:0: error: conditional compilation flags must be valid Swift identifiers (rather than '-D')
+// INVALID-COND-NEXT: <unknown>:0: error: invalid argument '-D-D'; did you provide a redundant '-D' in your build settings?