diff --git a/SConstruct b/SConstruct
index 3e2df39cfb..f3d65f01c4 100755
--- a/SConstruct
+++ b/SConstruct
@@ -328,7 +328,9 @@ if main['GCC']:
         error('gcc version 5 or newer required.\n'
               'Installed version:', main['CXXVERSION'])
 
-    # If not disabled, set the Link-Time Optimization (LTO) flags.
+    # Add the appropriate Link-Time Optimization (LTO) flags
+    # unless LTO is explicitly turned off. Note that these flags
+    # are only used by the fast target.
     if not GetOption('no_lto'):
         # g++ uses "make" to parallelize LTO. The program can be overriden with
         # the environment variable "MAKE", but we currently make no attempt to
diff --git a/src/SConscript b/src/SConscript
index 831f5c6484..47aa2eaf9e 100644
--- a/src/SConscript
+++ b/src/SConscript
@@ -1435,8 +1435,11 @@ if env['GCC']:
     # the optimization to the ldflags as LTO defers the optimization
     # to link time
     for target in ['opt', 'fast', 'prof', 'perf']:
-        ccflags[target] += ['-O3'] + env['LTO_CCFLAGS']
-        ldflags[target] += ['-O3'] + env['LTO_LDFLAGS']
+        ccflags[target] += ['-O3']
+        ldflags[target] += ['-O3']
+
+    ccflags['fast'] += env['LTO_CCFLAGS']
+    ldflags['fast'] += env['LTO_LDFLAGS']
 elif env['CLANG']:
     ccflags['debug'] += ['-g', '-O0']
     # opt, fast, prof and perf all share the same cc flags