diff --git a/zsh-syntax-highlighting.zsh b/zsh-syntax-highlighting.zsh
index fff47d1..52d35f2 100644
--- a/zsh-syntax-highlighting.zsh
+++ b/zsh-syntax-highlighting.zsh
@@ -28,8 +28,12 @@
 # -------------------------------------------------------------------------------------------------
 
 # First of all, ensure predictable parsing.
-zsh_highlight__aliases=`builtin alias -L`
-builtin unalias -m '*'
+zsh_highlight__aliases=`builtin alias -Lm '[^+]*'`
+# In zsh <= 5.2, `alias -L` emits aliases that begin with a plus sign ('alias -- +foo=42')
+# them without a '--' guard, so they don't round trip.
+#
+# Hence, we exclude them from unaliasing:
+builtin unalias -m '[^+]*'
 
 # Set $0 to the expected value, regardless of functionargzero.
 0=${(%):-%N}