diff --git a/bash/.config/bash/rc b/bash/.config/bash/rc
index ebe09d2..8f8da47 100644
--- a/bash/.config/bash/rc
+++ b/bash/.config/bash/rc
@@ -10,7 +10,8 @@
 # Case-insensitive globbing (used in pathname expansion)
 shopt -s nocaseglob;
 
-# Append to the Bash history file, rather than overwriting it
+# Append to the Bash history file, rather than overwriting it.
+# (HISTFILE/HISTSIZE/HISTFILESIZE/HISTCONTROL come from ~/.config/shell/exports.)
 shopt -s histappend;
 
 # Autocorrect typos in path names when using `cd`
diff --git a/shell/.config/shell/exports b/shell/.config/shell/exports
index 2603706..b530193 100644
--- a/shell/.config/shell/exports
+++ b/shell/.config/shell/exports
@@ -7,8 +7,14 @@ export XDG_CACHE_HOME="$HOME/.cache"
 # Default editor
 export EDITOR='vim'
 
-# Shell history file
+# Shell history (env vars both shells read; each ignores the other's by name —
+# zsh uses SAVEHIST, bash uses HISTFILESIZE/HISTCONTROL. zsh dedup is a setopt,
+# not an env var, so it stays in .zshrc).
 export HISTFILE="${XDG_CACHE_HOME:-$HOME/.cache}/shell/history"
+export HISTSIZE=1000000        # commands kept in memory (both shells)
+export SAVEHIST=1000000        # zsh: lines written to $HISTFILE
+export HISTFILESIZE=1000000    # bash: lines written to $HISTFILE
+export HISTCONTROL=ignoreboth  # bash: drop dups + space-prefixed
 
 # Global git config file
 export GIT_CONFIG_GLOBAL="${XDG_CONFIG_HOME:-$HOME/.config}/git/config"
diff --git a/shell/.config/shell/interactive b/shell/.config/shell/interactive
index e6f2b8c..81bc4f0 100644
--- a/shell/.config/shell/interactive
+++ b/shell/.config/shell/interactive
@@ -8,5 +8,9 @@ for _file in "${XDG_CONFIG_HOME:-$HOME/.config}"/shell/{aliases,functions,extra}
 done
 unset _file
 
+# Ensure the history dir exists; neither shell mkdir's it, so without this
+# $HISTFILE writes fail silently on a fresh host.
+[ -n "$HISTFILE" ] && mkdir -p "$(dirname "$HISTFILE")"
+
 # pyenv interactive shims (pyenv init - autodetects the running shell):
 command -v pyenv >/dev/null 2>&1 && eval "$(pyenv init -)"
diff --git a/zsh/.config/zsh/.zshrc b/zsh/.config/zsh/.zshrc
index 7fa9429..e1a8fd7 100644
--- a/zsh/.config/zsh/.zshrc
+++ b/zsh/.config/zsh/.zshrc
@@ -12,9 +12,9 @@ setopt autocd		# Automatically cd into typed directory.
 stty stop undef		# Disable ctrl-s to freeze terminal.
 setopt interactive_comments
 
-# History in cache directory:
-HISTSIZE=10000000
-SAVEHIST=10000000
+# HISTFILE/HISTSIZE/SAVEHIST come from ~/.config/shell/exports (shared).
+# Dedup is a setopt, not an env var (bash's HISTCONTROL=ignoreboth equivalent):
+setopt hist_ignore_all_dups hist_ignore_space
 
 # Basic auto/tab complete:
 autoload -U compinit